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North Cascades Dunite (Olivine)
The above series is designed to explore one key aspect of stone sculpture that is unique to the art form, its geology.
Why should you care about the geology of stone?
Granite is a magnificent rock that has adorned cities for centuries. It is treasured for its beautiful texture as well as its multitude of utility. It not only flaunts itself in polished monuments, statues and intricate sculptures, but provides foundations for buildings, curbs for streets and steps for stairs.
It is undoubtedly the world's dimension building stone and the stone of the world's bygone heroes and heroines. Brilliantine reds, pinks, blacks, grays, and whites continue to sparkle century after century as other stones turn to clay and dust. Hard granite is no stone for the weak hearted or the limp wristed; the beauty of the stone must be earned by hard work. Some of the most noted mountains in the United States are, by no mistake, granite massifs: Stone Mountain and Mount Rushmore, both with their carved historical figures; the Old Man in the Mountain, Mother Nature's carved face; Mount Monadnock; and, closer to home in the Pacific Northwest, Mount Index
Many carvers are intimidated by the difficulty of sanding and polishing basalt. This is entirely unnecessary. Soon you too will discover that deep space, raven’s wing glow within your own dark and crusty igneous chunks. Basalt is in fact very easy to finish if you follow these eight easy steps:
The English word jade has a circuitous derivation. It started with the Spanish expression "piedra de hijada", meaning the "stone of the loins", because it was claimed that this stone could cure diseases of the kidneys. This gave rise to the word nephrite, from the Greek word for kidneys: nephros. The French equivalent l'ejade eventually evolved into le jade, and its English translation, jade.
Ed. Note: The Stone of Heaven is one of the most revered natural substances in the world, such has been the case for centuries, particularly in Asia. What other mineral would make a Chinese emperor offer fifteen cities for a jade carving that he could hold in the palm of his hand or make Montezuma smile when he heard that the Spaniard Cortez was interested only in gold, since Montezuma's most precious possession was jade.
In the book, The Agony and the Ecstasy, Michelangelo is said to have draped the David marble in damp cloth after every carving session. What was he doing?
While I wouldn't begin to question Michelangelo's approach, I strongly suspect that description is more artistic license of the author than artistic technique of the sculptor. Damp cloth draping is essential when modeling in clay but as far as I can determine....
Here we share the experience and knowledge of those who have found their own answers to some of the inevitable and sometimes nagging questions forever popping up in our sculpture projects. Newcomers will find it useful and even those who have been carving for some time can never deny the benefit of a tune-up. (2013)
FINISHING SOFT STONE
By JoAnne Duby
Soapstone, Chlorite, alabaster, limestone, Pyrophyllite
I break the carving down into four stages:
• Clean-up, if it is a rough boulder stone.
• Rough out of design.
• Completion of the design, sanding up to 220 grit.
• With silicone carbide paper, sanding up to 320 grit, and then polishing up to 3000 grit. Wax it if desired or if it's going outdoors.
I find you can really move lines around till you get to 320 grit. To get a great finish on soft stone I very rarely use diamonds they are just too aggressive for soft stone. It's like taking a machine gun to a knife fight......way over-kill.
You need to clean up the carving area where you're going to do your finishing work. I use inter tube tires filled with sand as my sand bags (Learned from Camp B.) Then I put plastic bags around those. You want a clean environment and you want to rinse the area between sanding grits. Hose the table down, rinse and wash the sculpture with clean water after every grit; pretend it's an operating table. It's easy to pick up a rougher grit and put scratches back in your sculpture if you don't do this.
Remember to put your biggest effort in your lower grits. When you get to 320, we consider that to be polishing and in some instances you can stop sanding there when dealing with limestone; the soft limestone anyway.
I don't start with the wet sanding till I am at 220 grit paper. (Buy a good quality paper. Not Harbor Freight.) Auto body shops or car repair shops have wet and dry papers in the high ranges, 1000 to 3000. You can get great paper on-line from Norton, Pearl and many more.
Chlorite and alabaster I sand up to 600 grit or 800 grit, let dry for a day outside if it's warm or inside if cold, and then apply sealers.
To enhance or not to enhance - that is the question. Enhance if you like the look of your stone wet, use a natural sealer if you like the dry look to your stone.
For the dry stone look 511’s Porous Plus Sealer is the best, but it’s expensive, so I use 511 or 611 Miracle sealers or their impregnator.
For the wet look, my favorite is Tenax Ager. There are many sealers to choose from, very expensive to cheap. Talk to other stone carvers for their input.
Apply the sealer with clean brush or cloth, let stand on the stone for around 10 minutes. Do not do this in direct sunshine it can dry too fast and become like sticky glue. (If that happens just apply more sealer and wipe off.) Sometimes you need to apply the sealer twice. Read the back of the can; they really do know what they are talking about.
I finish with a rag wheel on a drill or a slow die grinder (key word SLOW) that I got from Randy Zieber at Neolithic Stone. I use a Chrome polishing bar with the Rag wheel to get the very polished look.
Soapstone, Chlorite, Pyrophyllite
I start with 220 grit and then go right to 400 grit then 800 and 1000 I skip grits with these because it so soft and 220 grit will become 320 grit when well used. For instance, I use a lot of pressure when I start the grit, then when I have sanded the whole piece; I do a lighter sanding with the used paper. Then finish the same as with the sealers on alabaster. I sometimes just use wax finishes, I'll warm the piece with a heat gun or hair dryer and apply the wax (for soap stones and chlorite only) I always wax if the piece goes out doors. You can get good waxes from your hardware store; even shoe polish is a great wax. The best is bowling alley wax. Many sources for that on the internet
Waxy, multi-colored alabaster has been the choice of stone for artists and artisans for millennia. It not only serves as the source of beautiful sculptures, but historically it provided utilitarian objects such as jars and casks. It was prized by the Assyrians and the Egyptians for its beauty. One of its most handsome and unique characteristics is its ability to pass light; imagine, a stone that can transmit light through it. While we sculptors use it for carving, alabaster's cousin, gypsum, is around us most everywhere we go and is handy on all of our workshop shelves.
Geology
Alabaster is one of several forms of gypsum, and it is both a mineral and a sedimentary rock. It is a hydrated calcium sulfate, Ca S04' 2 H20 that is found in many places throughout the world. It is a sedimentary evaporite deposit that precipitates from the evaporation of saline water. The ideal conditions for its formation are (I) a restricted arm of the sea, (2) intense evaporation, (3) replenishment by normal sea water and (4) gradual sinking of the basin.
Anhydrite has not been a widely popular stone, but its availability on the west coast of North American and the beauty of its finish is likely to result in more sculpture exbibits in the future. It has the pearly luster of alabaster and yet carves and finishes more like the harder stones.
Geology
Anhydrite is both a mineral and a sedimentary rock. Its name comes from the Greek for "without water"; essentially it is the anhydrous form of calcium sulfite (CaSo4). Anhydrite is the sister or brother of alabaster (gypsum), which is the hydrated form of calcium sulfate. Two molecules of water are attached to each molecule of calcium sulfate in gypsum.
Anhydrite commonly is found in white, gray, brown and light red or pink. It is heavier than alabaster, weighing in at about 187 pounds per cubic foot with a specific gravity of 3.0. One of the key differences between alabaster and anhydrite is the hardness: alabaster is 2 and anhydrite ranges from 3 to 3.5. It is insoluble in hydrochloric acid and sulfuric acid; however, it is easily attacked by water. in the earth, anhydrite converts to gypsum when it absorbs water; and in your yard, it will break down with facility if exposed to the elements.
Anhydrite is one of a group of rock-forming minerals called evaporites, so called because they form by the precipitation of the minerals from evaporating brines or salt water. The other evaporties are gypsum and halite (salt). They form in shallow salt water seas that are alternately submerged and de-watered. Beds of the rocks can be found in the thicknesses of a few hundred feet. Which mineral is precipitated at any time depends n the temperature, pressure and salinity of the water. At higher temperatures, anhydrite is the first one to precipitate, followed by gypsum, however, at lower temperatures, te opposite is the case. Halite is normally the last to form. In the laboratory, and presumably in nature, gypsum and anhydrite can be made to convert to one another by the changing of pressure and temperature. It is also known that anhydrite can be changed to gypsum by the addition of water, such as during the weathering process; and conversely, the reverse can be achieved by the baking or drying of gypsum.
In North America, anhydrite is found in the salt domes of Louisiana and Texas and in stratified deposits in Nova Scotia, New York, New Mexico and British Columbia. It is also in large layered salt deposits of Poland, Germany, Austria, France and lndia. It is not considered an important industrial mineral. In large deposits of gypsum, it is considered to be a contaminant. It is used as a source oj sulfuric acid, as a retardant for concrete, for a filler in paper and as a soil conditioner.
Quarrying
Although anhydrite is relatively hard stone, it is somewhat easy to mine because it si cut by numerous joints. Therefore, for the quantities needed for sculptural purposes, it is not necessary to blast to obtain. If blasted, this stone would probably shatter and much of the stone would be unstable. It is removed from the ground or rock face by hand tools or with a backhoe. The best method for determining the integrity of the stone is to tap the stone with a hammer and listen carefully for changes n the ring.
Working Anhydrite
Anhydrite is brittle and hand tool working is not recommended. Although a harness of 3 to 3.5 is not extreme, sculptors who have worked the stone definitely prefer the use of power tools for working this stone. Chisels tend to create small chips corners are commonly lost because an unexpected piece breaks off. The good part is that anhydrite unlikely to bruise in the manner that alabaster does.
It can be worked with a hand-held grinder as well as a stationary wheel, and the stone cuts very evenly and easily with such tools. Anhydrite takes well to a grinder, and carbide disks will show little wear after working the stone.
Anhydrite can be taken to a 70 to 600 grit finish. depending on the pattern of the stone, and buffed with tin oxide using a wet rag or a mechanical buffer. Of all of the colors, white produces the most lustrous finish although brown may have the most interesting patterns.
Flaws
Cracks and joints are not common flaws in anhydrite. In general, it is a solid stone. The white variety tends to be the most consistent in color and hardness. The brown stone can be more variable in hardness, containing scattered softer spots. Sometimes, small white spots may be present in the stone.
Although not exactly a flaw of the stone, a major weakness of all anhydrite is its susceptibility to water. It must be kept indoors before and after carving. If left outdoors, it will absorb water and start to deteriorate.
Safety
No particular safety hazards were reported for anhydrite; however, we all need to remember to protect out lung, eyes and ears at all times. Be a sage and safe sculptor.
Appreciation
Thanks to Randy Zeiber of Vancouver, British Columbia for his quarrying and carving expertise and Carol Way and Vic Picou of Seattle, Washington for sharing their carving experiences with me.
Editor's Note: I could not locate a picture of a sculpture done in anhydrite for this issue. I hope to have one for the next issue. This concludes the series on stone. I know I speak for the readers of Sculpture Northwest is expressing appreciation to Bill Laprade for this interesting and informative series.
Slate is a rather mundane, common stone that we remember from our school days. Recall those days when the teacher asked you to do your math problem on the blackboard (slate, in the olde days) and the dog had eaten your homework. Perhaps you could have pulled out your carving tools, turning it into an art class, and rendered a spectacular art piece right there in front of the class for a bit of diversion. In the hands of an artist, this stone is indeed anything but mundane. Reliefs of beautiful and varied texture can be rendered from this stone.
Geology
Slate is a metamorphic rock, found in many places throughout the world Its main constituents are quartz, illite, sericite and calcite, but other minerals such as plagioclase feldspar, chlorite, dolomite, pyrite and graphite are also found Where the slate is colored red, it probably contains a significant amount of hematite. Its particles are very small; less than 0.001 millimeters in diameter. The parent rock for slate is shale, which was formed from the deposition of mud (clay and silt). Slate is a very close cousin to argillite, also used for sculptural purposes, and associated with the Haida of the Northwest Coast.
Slate is moderately hard, but it is very brittle. Its durability is one of its chief attributes. Its unconfined compressive strength ranges from 7,000 to 10,000 pounds per square inch. Its very low porosity, less than 2 percent, is responsible for its impermeable nature and the reason that it has been used for roofing for centuries. It is difficult to assign a hardness to this stone, because it depends on the direction in which it is worked; however, it normally falls between 1.5 and 2.5.
Slate is formed deep beneath the earth's surface by the slow pressurizing of fine grained sediments, such as shale and claystone. The pressure increases from the addition of overlying sediment, slowly squeezing the water out of the pores. Then folding causes the individual mineral grains to realign and form parallel sheets. The resultant rock has very pronounced directionality, known as cleavage; that is, the rock will split easily in one preferred plane. The plane of cleavage is usually not the same as the plane of the bedding, and in fuel, the original bedding of the stone may be very hard to discern. In natural deposits of slate, veins of quartz and dikes of intrusive igneous rock are not uncommon, and the rock may be severely fractured along fault zones.
Although black is the most common color of slate, it is also gray, purple, green and red. It is found in France, Fiuland, Scotland, Peunsylvania, Vermont and California. In Washington State, poor quality slate is present in the western part of the state, but commercial deposits are found in Stevens County in the northeastern corner.
The highest quality slate is used for blackboards and pool tables. Because of its high electrical resistivity, it is used for switchboards and electrical panels. It is also used for mantles, flagstone (interior and exterior), haseboards and roofing. As there is very high wastage in the production of dimensional, the waste is crushed and used for roofing granules, insulating material known as rock wool, and for filler for paint, linoleum, acoustical tile and brick.
Quarrying
Because of the extreme directionality of the cleavage in slate, quarries sometimes continue at near-vertical angles to depths of 700 feet. Drilling and blasting are utilized to remove the weathered rock, but discontinued thereafter owing to the sensitivity of this brittle rock to shock.
Primary cuts are made by channelling or wire saw. Individual blocks are then separated from the quarry floor by splitting parallel with the cleavage. Large blocks are then subdivided in a similar manner. Due to the brittle nature of the stone, the percentage of waste in a dimensional stone quarry may be 60 to 90 percent.
Working Slate
The most common manner of carving slate is in low relief; however, it can be used to create a truly threedimensional sculpture. Isamu Nognchi prodnced some large scale pieces with thick slabs of slate, and Barbara Hepworth fashioned a piece called "Two Figures" in which she pierced two large pieces of slate in a stunning slate sculpture.
Slate can be obtained from a salvage yard or thrift store where it may have been part of a blackboard or pool table. These are the highest quality slates available. Alternately, flagstone slate can be bought from a stone yard or landscaping materials supplier.
In relief, slate can be worked in a similar manner to wood. A drawing is copied onto the flat slate surface, either by freehand or with carbon paper. The outline of the drawing is scored deeply with a very sharp instrument. Although a diamond tool may be the most efficient, any sharp steel tool will do. It is best to pull the instrument toward you to maintain control ofthe tool and to avoid chipping. The subject is then highlighted in relief by carving from the outside into the incision. Great care must be taken to avoid advancing past the incision, because the layered slate will chip easily. Standard softstone carving tools can be use for this stage, such as flat chisels, ronelles, and toothed chisels.
After completing the outline, the interior body of the sculpture can be modelled and curved with rasps and rifflers to create effective shadows and a sense of threedimensionality. Polishing is started with 220 grit and can proceed to 1200 grit to obtain a high sheen. If desired, the surface can be waxed andbuffed Outlines should be retraced with a sharp tool to remove the wax in the grooves.
Texturing can be very effective on slate. This can be accomplished with a rasp, a toothed chisel or even a frosting tool, provided that the sculptor is very light-handed wooden mallet would be advisable for such work. Slate can be cut with a hack or coping saw, but care should be taken that the brittle nature does not cause the stone to break in a place not desired.
Flaws
The chief flaw in slate is the separations between the individual layers along the cleavage. Look very carefully at the slate to see if there are any weak planes. As with other stones, tapping the stone with a small harurner or the butt-end of a chisel will tell a tale, but tap gently with slate.
Pyrite and quartz crystals are much harder inclusions that will ruin the integrity of the carving surface, so if some are showing on the surface, there very well may be some more on the interior.
Safety
Because no hammering and power tools are reqnired, no eye protection in required with slate; however, the stone is finegrained, so a mask would be prudent if you are making dust.
Appreciations
Thanks to artist Ward Lynch of Everson, Washington for sharing his slate carving experiences with me.
Introduction
Sculpture, ahh, sculpture. Poetry in form and light. I was introduced to bronze and sculpture together in 1980. Coming from a 2-D background where I was employed as a scrimshander (engraving on mammoth ivory), I was initially attracted to sculpture as a way of stretching artistically and bronze as a method of preserving the hundreds of hours I have a tendency of dumping into my work.
The journey that began back then has become the core of my experience. It has led to the founding and operation of North West Artworks, an art casting foundry in Sultan, Washington, that I helped establish with my father and brother. Casting for others has introduced me to many different styles and how bronze relates to them. In my own work, bronze's nature and soul play an important roll in the statement I want to express. My intention for this article is to not ouly illustrate the process of lost wax casting, but also that bronze is more than just a material to reproduce sculpture.
Characteristic
Bronze is 50% to 93 % copper. There are many kinds of bronze and brass alloys, the differences lying in what's been added to the copper to change undesirable characteristics such as low fluidity, gassing and weak castings. Common additions include tin, zinc, lead and silicon.
Most art casting is done in a silicon bronze, a lead-free alloy.Evedur and Hurlaloy are the two types of silicon bronze available. The main difference is the amount of zinc present. Each foundry has its own preference (Evedur being ours), but the desired characteristics are basically the same: fluidity, attention to detail, reparability and finish.
Bronze is bearing metal, which means it is soft and slippery or resistant to surface friction. This gives the metal a unique tactile quality. It is very malleable and can endure pounding and bending (cold work) without tearing.
Bronze is permanent (our insurance company claims it has a life of. 100,000 years at the bottom of the ocean). Bronze is musical (325 Ib. ingot resonates when dropped).
There are many ways of finishing bronze using chemical patinas. Some can accent the form and texture of a piece; others can give a depth of color rivaled only by stone. A faux granite, marble, and sandstone can be achieved with patinas.
Bronze is a structural material making it possible for expanded delicate forms (fingers, etc.) and a great versatility in scale. These and other characteristics make bronze an ideal sculptural medium.
History
Bronze has been linked into the evolution of civilization since its development 5,000 years ago. In the Near East, it was discovered that the addition of tin to copper created an alloy that was extraordinarily versatile in the production of tools, weapons, housewares and art. The lack of tin in the Near East created an expanding trade network that eventually encompassed Europe and the Far East.
The technique of lost wax casting is almost as old as bronze and has remained relatively unchanged until the 1960' s, when high-tech, high-temperature ceramic investment was introduced by the aerospace industry for use in precision castings. This, coupled with the development of silicon and urethane rubber used in the molds, made high detailed casting more achievable. But even with the modern advancements, art castings remain a hands-on, labor intensive, highly skilled craft.
Process
There are two styles of lost wax casting. The difference is in the type of investment in which the wax is encased: traditional plaster investtnent and ceramic shell. Since we use the ceramic shell, the outline below addresses that method:
1. The original artwork is sculpted by an artist in wax, clay. plaster, wood, or stone.
2. From the original artwork (or from a found object), a reusable master mold is made. This master mold consists of a flexible inner mold and a rigid exterior mold or mother mold. The rigid mother mold is designed to hold the flexible inner mold in place and retain its shape. A single master mold can take from three days to several weeks to complete. The flexible inner mold is usually made from polyurethane or silicone rubber and the rigid outer mold from fiberglass or plaster.
3. From the master mold a wax pattern is made using a slush technique (i. e., pouring molten wax into the mold, allowing it to cool slightly and then pouring out the excess wax). This process is repeated several times to achieve the proper thickness (1/8" to 3/16"). Wax patterns for small pieces are usually cast solid. After the wax pattern is removed from the mold, it is chased (correcting in'Iperfections in the wax form) and dissected into pieces to aid in the casting process. This can take a week or more to complete.
4. Wax sprues, gates and risers are added to the wax pattern. They direct the way in which the wax evacuates or leaves the invested pattern and metal enters or fills the ceramic shell, and are crucial in controlling shrinkage of the sculpture as the metal cools.
5. After the wax pattern has been sprued, it is then chemically cleaned and invested (invested means creating a secondary waste mold around the wax). The waste mold consists of a "dip and stucco" technique using a silica slurry with stuccoed layers of imported sand. The result is a fireproof ceramic shell surrounding the pattern and the sprues, gates and risers. One layer of slurry is applied each day for at least eight days.
6. Burnout involves removing the wax pattern from the ceramic shell investment by using heat and pressure. The wax is evacuated when the cerantic shell is flash fired (plunged into an 1800 degree F furnace for 1-112 hours). Hence, the term, "'Lost Wax" .
7. Inspection of the evacuated shell takes place after it has cooled. The shell is vacuumed to remove carbon ash and patched if any cracks were created during burnout.
8. The pour involves melting the bronze in a silicon carbide crucible or cup. The molten bronze is then poured at 1950 to 2150 degrees F into the shells, which have been preheated to approximately 500 degrees F (preheating the shells reduces the chance of flashing and metal shrinkage).
9 The finish work involves:
(a) Knockout, or removal of investtnent;
(b) Degating, or removal of the sprues and gates;
(c) Welding and refabrication of the sculpture;
(d) Chasing the sculpture or fixing any casting flaws;
(e) Cleaning or sandblasting the sculpture;
(I) Patina work or aging, coloring and sealing the metal;
(g) Mounting the sculpture or making the base and fastening the sculpture to it.
Smaller sculptures can be cast in one piece, whereas larger or complex sculptures must be cast in many sections and refabricated. "Temple," an 80% life sculpture (pictured), was cast in seven pieces.
Turn around time is usually four to eight weeks (without mold work), depending on the scope of the project and the work load of the shop.
Costs are hard to generalize, but a 9" solid standing figures runs around $120, whereas a life-sized fignre is in the range of $4,000 to $6,000 without mold work. Costs can be cut dramatically with the artists participating in the labor.
Summary
Bronze offers an artist an expanded arena to express hislber vision. I am conducting a continuing series of workshops (see the paid advertisement in this newsletter) to introduce the fundamentals of reproducing sculpture. The artist can enter at any phase of the workshops to gain experience in a particular area of interest. The workshops are intensive, but give the artist a practical fundamental base on which to build.
Questions
If you have any questions concerning the current workshops or future workshops you would like to see, please contact me directly at: PO Box 777, Sultan, WA 98294; (360) 793-0783. If you need information about having your pieces cast, please contact: Todd Pettelle, clo NW Artworks, PO Box 658, Sultan, WA 98294; (360) 793-2412.
Conclusion
I would like to thank Bill Laprade and Sculpture Northwest for giving me the opportunity to contribute my perspective on this wonderful, though often misunderstood, medium. 1'd also like to express the privilege I feel to be a part of this exceptional organization. Welcome back, Bill.
Sandstone has been a reliable utility stone throughout the centuries. Many cities, both ancient and modem, take advantage of its fine qualities. It is easy to quarry, found throughout the world, is relatively easy to shape and carve, and resists erosion in most climates. While it is limited in colors, it is commonly uniform, compared to other stones, and therefore provides the architect with a useful building stone.
Geology
In very basic terms, sandstone is a sedimentary rock that is nothing more than cemented sand grains. If the grain size gets too large, the rock is a conglomerate; if the grains are too fme, the rock is a claystone, shale, slate or argillite. There are several types of sandstone: arkose, arenite, graywacke, orthoquartzite and protoquartzite. The classification depends on the kind of cementing agent and the percentage of quartz and feldspar sand particles. The chief types of cementation include silica (quartz, opal and chalcedony), calcite, dolomite, clay and limonite. The cementing agent can either be deposited at the same time as the sand particles or at a later date.
The sand grains themselves can be derived from any other existing rocks that are nearby, and they may be any shape, although they are commonly rounded to subrounded owing to the collisions with other particles during transportation. They may have accumulated in ancient sand dunes, on river bottoms, in the shallow portion or deltas of fresh water lakes or in a shallow marine environment. Very slowly over millions of years, the deposits of sand are compacted by overlying rock strata. The pressure and the cement cause the rock to gain strength. As a general rule, the older the rock, the higher the strength.
Because sandstone is deposited in environments where organisms live, fossils are common. For similar reasons, concretions, hard nodes with interesting shapes, are also found in sandstone. The concretions themselves are sometimes mined and their interesting shapes are objets d'art.
As a sedimentary rock, it is deposited in layers, and is commonly interbedded with shale, limestone and coal. Where the four repeat in sequences, they are called cyclothems. Where higher depositional energy is involved, the gravel or cobbles change the rock designation to conglomerate.
As a rock (as compared to a mineral), sandstone does not have a designated hardness. Its hardness ranges considerably because of the wide range of cementing agents and degrees of weathering. Caveats aside, sandstone probably ranges from 3 to 6 in hardness. There are, of course, softer sandstones; however, they would probably not hold any sculptural detail and would spall badly in the elements. The hardness of sandstone is nonnally expressed in terms of its unconfmed compressive strength; the strength obtained by compressing a cylindrical piece of the stone to its breaking point. Unconfmed compressive strengths of stone suitable for buildings and sculpture are between 5,000 and 30,000 pounds per square inch (psi). Wilkeson Sandstone is reported to be one of the strongest sandstones in the world. Sandstone weighs between 136 and 166 pounds per cubic foot.
Sandstone is most commonly brown or gray; however, white, yellow, green and red exist. Can you guess what rock type are the "brownstones" of eastern U.S. cities? Some sandstone has layers or streaks of red iron oxide, which may make it attractive for sculpture, but not desirable as a building stone.
Its most common uses worldwide are in buildings, curbstones, bridge abutments and retaining
walls, because sandstone can be quarried relatively easily to very close tolerances. It can be pulverized into sand particles to use as sandblasting material or foundry sand. The hardest sandstones have been used as grindstones and sharpening stones.
Quarrying
Sandstone is extracted in large open pit surface mines, generally from large faces of exposed rock. Because of its stratification, it naturally divides in one dimension. The somewhat horizontal bedding provides a convenient plane on wbich the rock breaks. Planes of weakness in the other two planes commonly develop during compression or tension of the earth's crust. However, these planes of weakness may not be the correct size for building or sculptural stone. Therefore, cutting, drilling and light blasting are sometimes required to remove the stone.
In Washington State, Wilkeson, Tenino and Chuckanut sandstones have all been removed by cutting channels or slots in the rock and then drilling a row of holes aloug the bottom of the channeled rock. A row of drill holes across the back of the channeled section also separates the stone from the mountain. The width of the channels can be varied to render different thickness of slabs or blocks. Feathers and wedges can be used to bring the stones closer to the desired size. Tbe need for carbide or diamonds for the drills is governed by the strength of the cementing mineral.
The rectangular blocks of stone are then milled by gang saws and planers to a predetennined size that closely fits the fmal carved stone. Carvers of architectural stone use a multitude of models to copy.
Working Sandstone
Sandstone is chosen commonly for its uniformity of color and grain size. A unifonn block is essential for a good sculptural stone. Some of the most common flaws in sandstone that are unique to that stone are coal seams, fossils and concretions. In addition to being unsightly, the coal seams are weak and can cause the piece to split. Fossils can either be harder thau the stone or much softer; if softer, they can fall or spall out leaving a hole in the finished piece. Concretions are hard nodes within a softer rock that fonn around a small nuclear particle and bonded with a harder cement, commonly iron oxide. As with many rocks, small seemingly undetected fractures in the stone can result in the splitting of the stone after it has been worked for some time.
Sandstone can be roughed out with a diamond or carbide skill saw. A point can be used to take the shape within about l/2-inch of tbe final shape. Shaping is then accomplished with a toothed chisel, flat chisel and a cape chisel, a narrower version of a flat chisel. A "bull-nose" chisel is used to create concave surfaces. Sandstone carvers have traditionally used wooden mallets instead of iron or steel. The wooden mallets are strong enough to work sandstone and yet they reduce the noise and seem to absorb much of the energy before it reaches the hand and arm.
Smoothing of sandstone can be perfonned witb different implements, depending on the desired final effect. Initially, a carbide scraper or rasp is used, and then final polishing can be done with another piece of sandstone or with a diamond file. The latter is definitely recommended when working with Wilkeson Sandstone.
Sandstone can be either an indoor or outdoor stone, the main differentiating factor being porosity. If the stone has a high porosity, such that water can fill the voids, it is likely better indoors. Left outdoors, moisture and freeze-thaw would soon soften the surface of the sandstone and ruin any details. Look at a piece of sandstone on a building sometime and note the occasional scallop out of the stone facade. Many of the older buildings of Europe require restoration after a century or two. The most effective deterrent is periodic cleaning of the stone.
And remember! Keep your goggles and mask on. The dust is very fine grained and more than likely contains silica. Silicosis can be debilitating and even fatal.
Appreciations
Thanks to stone carver Keith Phillips of Tenino, Washington for sharing his knowledge and expertise of sandstone with us. Keith's enthusiasm for the history of quarrying and carving of sandstone are an inspiration to all who meet him.
Barite is a horrible name for selling stone. It has no cachet whatever. If anything, the name has the ring of something you don't want even close. It sounds radioactive. Before now, no one has even suggested using barite as a carving stone.
Here is some information on a new stone for the sculptor. Barite, mined worldwide, has many industrial applications. Barium-the element derived from barite, the mineral-is used in the manufacture of glass and paint and is used as "drillers' mud" at oil rigs. It is used medically. In diagnostic enemas, doctors don't hesitate to put it memorably close to patients. Unless you drop the heavy stuff on your toe, barite is no more harmful that most any other rock. When I inquired with OSHA, I was told it could be considered benign. It is not radioactive. Too bad barite sounds like something that could light your bones green. Terrible name. There has to be something better, a trade name.
Barite is very seldom found pure in nature. It typically comes mixed with other minerals of varying nasty hardness and ugly colors. This explains its lack of history as a sculpting media. Different, the barite from Prince of Wales Island is virtually pure as found. A report of chemical analysis conducted for past property owners by a private metallurgical Jab describes the barite as "a finely crystalline white rock containing no visible impurities." Alaskan Barite is typically Ivory Soap white but has occasional blue-grey, lavendar, and gold tones. For so dense a mineral, it is surprisingly translucent. With a hardness similar to that of alabaster, it carves easily with hand tools. It comes from a deposit far too small and remote for commercial barium production.
How about calling it "Alaska Heavy Stone?" The name "barite" comes from the ancient Greek word for heavy. Its weight is perhaps its most distinguishing characteristic. Barite is 4.5 times heavier than water. By comparison, calcite, the main component of marble, is 2.7 heavier. When you place a sculpted piece of barite on the table, it wants to stay put. I used it as a ballast in my boat before I could afford pigs of lead. Because of its great relative weight, barite might make excellent base material for sculpture of other materials.
It has been hard to get people to try it. Janet Willing was the first to take the chance. A few unwillings have tried it, usually convinced only after great brow beating on my part. 1 asked Nicky Oberholtzer to write her appraisal.
Barite is a very pleasing stone to carve. It responds well to the die grinder and the angle grinder. For beginners, who are using hand tools, it is ver)' easily worked. Caution should be exercised when using chisels as the stone is fairly brittle and more may come off than you planned. For those who hate sanding and polishing, the stone is a welcome surprise because it takes less effort to sand than most and the results are immediate. It takes an incredible shine without much effort und is silky smooth to the touch by the time you have finished with 220 grit.
Nicky is now recommending barite to her students. But. what to call it? How about: "Alaskan Wonder Stone?" No, that one gets a finger down the throat.
l once had on the boat a young intern geologist with the USGS. From Texas, he identified the mineral "BAY-rite." For the rest of our trip his veteran colleagues dubbed him "the BAY-rite kid."
Alaskan barite comes from the tip of a penn insula that protrudes into a very open area of ocean. Like most beach cobbles (note the barnacles) the stone can only be gathered when the seas are at their calmest. The location might be accessible only thirty days a year. Typically, I anchor my bigger boat in a protected cover about a mile away and go to the barite site in my skiff. If you happen to be there at a very low tide, you can also gather abalone and rock scallops. That happened once.
My first two attempts to collect there this year were unsuccessful. Twice I believed a favorable weather report. Twice I was foiled by the seas-the waves pounding on the exposed beach would have pooped the skiff at the landing or swamped it at sea had I dared a heavy load. The location is seven hours by boat, one way, from my home port of Craig. A lot of time and diesel were burnt for naught.
"Bear-ite" might work. Think of the possibilities if I could get the native population here to use it, instead of soapstone, to carve polar bears. In spite of barite's near perfect color, all my attempts in this direction have failed. I've heard a similar story of a Canadian sculptor who failed to get Eskimos to work a beautiful white marble in their back yard.
I did not use the Hyak on my third attempt. A couple of fishermen, who live on a boat moored near mine, offered the hire of their backs and their boat to gather stone. Better than my boat for the chore, theirs had a large fish hold and a boom that could be used to swing aboard tone delivered by skiff from the shore. The trip took longer than expected. By the time we got to the location, the tide had already covered most of the barite on the beach. The tide was not going to be low enough again to gather stone until around mid-night. We anchored and discussed possibilities. It was either gather stone in the dark of night with a flashlight or wait until around noon the next day. They said they had to be back in town and offloaded before a pending commercial fishing opening. We set the alarm for eleven p.m. and crawled into our bunks for the couple hour wait for low tide.
The tide was still dropping when we got to the beach. It was necessary for one of the fishermen, wearing chest waders, to remain standing in the surf to hold the skiff-it had to be kept in water shallow enough to be loaded but also deep enough for it to not "high center" on one of the random boulders of the intertidal zone. The other fisherman and I carried barite cobbles in the dark, holding little plastic flashlights between our teeth. We carried the stones, one or several at a time, out into the water to the tops (sometimes over the tops) of our rubber boots. The man in the chest waders, splashing phosphorescence, relayed the arm loads of stone to the side of the skiff, where he placed them over the gunwale.
"BARITE." It's a lousy namefor a finecarving stone. but, I'll just have to accept it. Grin and barite. '"
Notes from the 6/20/00 membership meeting on the topic: “Found Stone”
Soapstone deposits on the road to Lake Wenatchee, WA. You must get a Forest Service permit from the Ranger Station (509 763-3103) to collect it. They can also tell you where to find the stone. The permit is about $10 and the charge for stone is about $3/cubic yard. You can drive very close to the stone deposits. The soapstone comes in many colors — light to dark chocolate, greens, golds. It has been tested for asbestos and is believed to be asbestos-free. Some Serpentine can also be found.
White mystery stone on the way to Lake Wenatchee, WA. Past the ranger station on the road to Lake Wenatchee look out for a quarry with snow white stone. It’s harder than alabaster. You can’t just take it, but you can talk to the folks at the quarry about its availability.
Marble and more, near Kettle Falls in northeastern Washington. Near the Canadian border, on the east side of the Columbia River, right near the road is an inactive quarry with marble — white with green and gold flecks. Nearby, you can also find brucite, red marble, and pink marble. While in the area look around for other inactive quarries.
Serpentine everywhere. There is lots of serpentine all over. Look for an outcropping 7 miles north of Olmac. Look in Kititas county, and look in the Mt. Stewart Range. Note: serpentine can have arsenic inclusions.
Jade by Teanaway River, about 2 hours east of Seattle area, north of Cle Elum.
Limestone. At Miller Quarry in Goldbar, WA. Active quarry, some carvable limestone for $0.01/pound. They also have basalt. Look for another limestone quarry on the south fork of the Skykomish River, on the way to Index, WA. The limestone is dark with light streaks.
Sandstone. You can find black sandstone on lots of beaches. Look for a nice, creamy-textured one in Cowichan on Vancouver Island, Canada. Tenino, WA, has a sandstone quarry also.
Basalt. West of Yakima, WA, by the Naches River, look for basalt columns. If you’re boating on the Columbia River, you can find lots more basalt.
Dumpster stone. NW Marble and Terrazzo, in Bellevue, WA, at intersection of I90 and Richards Road has scrap dimensional stone that you can take from their dumpster. Types are those used for countertops, etc. Similar stores in your area may also have scrap stone available.
Collecting free or almost-free stone has a price — time, energy, risk of injury, car wear, etc. For many, finding stone this way is rewarding because they feel more connected with the stone and the earth finding it in its natural setting, there is less environmental impact and the forms are natural.
See also the book: Gem Trails of Washington
White, creamy limestone has been a staple of Pacific Northwest sculptors since 1992 when 6 tons of Utah oolitic found its way to the Northwest Stone Sculptors 5th annual carving symposium. It owes its continued popularity (10 tons at the 1993 symposium and many more tons subsequently) to its ease of carving, low cost and wonderful finished demeanor. It is indeed a “poor man’s marble,” both genetically and artistically. With sweeping curves and shapes, limestone casts beautiful shadows and interesting lines.
Geology
Limestone is a rock that contains 50 percent or more calcite (calcium carbonate, CaCO3) and dolomite (magnesium calcium carbonate, MgCaCO3), of which calcite is dominant. It is the sedimentary parent of the metamorphic rock, marble. In very simple terms, it is a rock from which lime can be produced. Although it is defined chemically, the calcium carbonate can be formed in more than one way:
The most commonly utilized limestone is oolitic or compact limestone that is formed from marine oolites or ooliths. Ooliths are small round or oval bodies, 0.25 to 2 millimeters in diameter that form concentric circles and/or radii of calcium carbonate around a nucleus by chemical precipitation. The nucleus may be a shell fragment, a small piece of algae, or a quartz sand particle. It is important that the oolith be continuously wave or current agitated, so concentric growth can continue.
The ooliths eventually become heavy enough to settle to the ocean floor, accumulate in thick layers, and over geologic time, through the pressure of the overburden, form limestone that is relatively compact and uniform. Just imagine; all those oolites huddled together at the bottom of the ocean waiting to be discovered by a stone supplier. Their growth is similar to the growth process of a hail stone. Another type of precipitate is travertine, in which calcium carbonate precipitates out of a cave of spring water and forms interestingly shaped and colored rock. Among others, this is the type of rock that forms stalagmites and stalactites in caverns. This rock typically contains voids, because of the irregular way in which it is deposited. Biologically formed limestone includes tufa, which are small calcium carbonate secreting fresh-water organisms, and reef-building corals. Both of these rocks are beautiful in their natural state, but are not considered to be carving stones.
Limestone can be found in several colors: white, brown, red, and yellow. Although the hardness of this rock can vary from very soft (1) to the hardness of 6, the most common carving limestone is about 3 to 4. The dominant mineral is calcite, with secondary dolomite and aragonite, but there are small quantities of chalcedony, quartz and other silicates.
Limestone is one of the most susceptible rocks in the world to chemical weathering; for instance, consider the fact that all of the great caverns in the world are carved by Mother Nature’s groundwater from limestone. Sculptures and building stones of limestone are particularly vulnerable to degradation in areas with acid
rain.
Limestone has a wide variety of uses other than artistic. It is used as crushed stone for roads and embankments, a dimension stone, a fluxing agent for smelting and refining iron and other metals, a component in plaster and mortar, in the production of chemicals, an ingredient in paper and glass making, a soil conditioner, a water softener and most importantly, the prime ingredient in cement.
Working Limestone
Because there are so many types of limestone, it is difficult to describe the carving of all of them. The softer limestones, especially those that are biologically formed, such as tufa and coral, are not used for carving, because they are fragile and brittle. Although weak corals are not useful for carving, some beautiful metamorphosed (fossilized) corals can be carved with diamond power tools. The coral designs are spectacularly preserved in the limestone.
Travertine can be an attractive stone for sculpture with its random voids. The voids can fit into the piece or just add to the ambiance of it. The voids do cause complications in the working of the stone. It becomes very problematic to work this stone with hand tools, because chisels create spalling around the edges of the natural holes in the stone or they may open up new holes that are just below the surface. Once these holes are rendered ragged by chisel marks, they are very difficult to erase, because they are below the working surface. It is essential to work this stone with power tools, preferably grinders and burrs.
Oolitic limestone is a perfect stone for beginners and expert alike. Because of the uniform method in which it is laid down, it has uniform color and hardness. It has very few surprises; something to be prized! Although it may contain some scattered iron sulfide or quartz, it is mostly pure carbonate or dolomite. The few joints or cracks in the stone can be exploited when breaking the stone into smaller pieces. Fortunately, upon careful scrutiny, even hairline cracks can normally be spotted in oolitic limestone.
This limestone can be worked with hand or power tools. Roughing out the form can be accomplished with a point, and then followed with a toothed chisel to within 1/2 to 1/8 inch of the finished surface. The grooves of the toothed chisel can then be eradicated with a flat chisel. With various grades and shapes of rasps, the final touches can then be applied. Surface smoothing can then proceed by using 200 to 400 grit wet-dry sandpaper. Paper finer than 400 grit yields very little return for the effort.
Texturing can be applied to oolitic limestone with wonderful results with a bushing hammer or tool and a toothed chisel. Using a carbide-tipped drill bit for a base pin hole, the limestone cuts like butter; be careful not to drill too deeply.
Although some limestones may be able to take the outdoors year-round, it is probably not advisable as a blanket practice. Owing to its moderate porosity; it can absorb water and suffer from freeze-thaw. A sealant is commonly applied in two coats to prevent penetration of water. As mentioned above, in the long-term, it is one of the most vulnerable of stones to acid rain attack.
Similar to marble, there are many reports regarding the benign dust of calcium carbonate-bearing limestone. However, don’t be too cavalier, because there are impurities, one of which is silica. So be safe and wear a mask, and keep your goggles on. You have only one pair of eyes.
Soapstone has become universally used as a carving medium by beginners and experienced journeymen alike, as well as those sculptors who appreciate its ease of working and its brilliant finish. It can be rapidly worked in detail with hand or power tools and can be brightly polished in beautiful hues. In its natural condition, it is earthy and mundane; one wonders why some sculptor first started to work this stone.
Geology
The geologic term for soapstone is talc or steatite; the two terms are synonymous. Talc is the name that you will find in a book of minerals; however, steatite will commonly be listed in the description. Reportedly, the term steatite was used commonly during World War II to describe massive and machinable talc that could be turned into strategic products such as insulators and metal molds. There are many grades of soapstone, ranging from hard to soft and dense to flaky. Soapstone has a minimum of 20 % talc, but can contain several subordinate minerals.
Talc is the indicator mineral for a hardness of 1 on the Mohs Hardness Scale. This mineral has a greasy feel, and is a very poor conductor of electricity and heat, the reason it is used as an insulator.
Minerals that commonly are found in association with soapstone are chlorite, serpentine, magnesite, antigorite, pyrite and enstatite. Another mineral that is similar and can only be distinguished from talc by chemical or x-ray analysis is pyrophyllite, hydrous aluminum silicate.
Talc can be formed in two ways. It is the product of alteration of other rocks and minerals; or it has been metamorphosed. It can be regionally altered dolomitic limestone or altered igneous rocks. Therefore, talc is commonly found in two different environments: massive deposits or veins. The alteration from the original rock, such as olivine, to talc is made in a water-rich environment at moderate temperatures of about 1300 degrees F. Commonly, the vehicles for the intrusion of water are shear zones along faults.
While the formation of talc is not a direct result of the movement, the travel of water along the zone of weakness completes the process. The largest bodies of soapstone come from regional metamorphism (burial) of large deposits of dolomitic limestone, a calcium magnesium carbonate.
Some of the larger bodies of soapstone in the world are located in Ontario Province, New York, North Carolina, Georgia, California, Austria, Madras and Italy. The smaller bodies tend to be narrow veins related to shear zones or igneous intrusions, and are commonly found in Washington, Virginia and California.
Colors vary considerably: buff, brown, gold, red, orange, black, green, blue, and black with white marbling. Frequently, the outside of the rock may be red and this iron-oxide weathered zone will give way to another color on the interior of the stone. In the Pacific Northwest, the most common colors tend to be buff, brown and green.
Quarrying
Soapstone is obtained in several ways, depending on the size and accessibility of the deposit. One method with which many of those in the Northwest Stone Sculptors Association are familiar, is hunting for cobbles and boulders on the slopes of a landslide deposit near Lake Wenatchee. (A commercial mining company now formally claims this deposit, so it is no longer open to us, but as of Oct. 2000, one of our members found another deposit, which is not on that claim.) The soapstone chunks are scattered about the landscape, and a shovel and crowbar are necessary tools to liberate them. Sometimes small pieces can be found that are the right size to just toss in the back of the truck, whereas other larger behemoths must be cut in place with a bow or chain saw to gain a manageable piece. Some of the larger boulders have soapstone on the outside, but then transition to another harder rock type on the interior.
In vein deposits, a backhoe is commonly used to loosen soapstone chunks, following the line of the vein. In the massive deposits or in very wide layers, the materials can be worked with a dozer and a backhoe together. It is common for the quarry operators to use the natural joints and weak planes in the formation to loosen the rock. Each piece is then trimmed into sizes ranging from 5 to 1,000 pounds, using chain, band and bow saws. The waste materials from larger quarrying operations can be used for such things as cooking stones or foot warmers, and as additives in paint and cosmetics.
The Asbestos Quandary
Is there asbestos in the soapstone that we chip and pulverize right in front of our faces? The answer is yes and no. Asbestiform laths are obvious in some of the soapstone that we see; however, the asbestos particles do not have to be visible to the naked eye or even magnifying glass to be harmful. It has been reported that roughly 40 to 50 percent of the soapstone contains some asbestos. The only way to know for sure is to have the stone tested by a laboratory. Soapstone from the Lake Wenatchee area and Marblemount tested clean this year. However, one stone does not a quarry make; different parts of a quarry can contain different accessory minerals. To be on the safe side, if you are not going to test each piece of stone that you work, treat the stone as if it does contain asbestos and wear appropriate breathing protection.
Tools and Flaws
Soapstone can be worked with both hand and power tools. The watchwords should probably be, "Don't break the tea cup with a sledge hammer." Tools used on soapstone should be appropriately suited and sized to this very soft rock. The use of a large hammer or chisel can cause the unwanted splitting of the rock along an unnoticed plane of weakness. It is preferable to be on the safe side by using smaller hand tools. Because soapstone can usually be removed readily with rasps and rifflers, they should be used in the vicinity of a linear flaw.
Rasps, rifflers and then sandpaper are the orderly progression for the smoothing and polishing process. Water should be liberally used during the sanding to aid in the polishing and to keep the pores of the wet/dry sandpaper unclogged.
It is common for there to be harder spots in the stone and even small pieces of iron pyrite. That will put a dent in your rasp! On the other hand, there are reports of finding small voids in soapstone, perhaps from the weathering of sulfides.
An interesting development was reported in a 1992 edition of Sculpture NorthWest by Patty McPhee regarding the firing of finished soapstone pieces to cone 4
(about 1,600 degrees F). She reported that this process turned the soapstone pieces very hard and darkened them. The firing increased the hardness from 1 to about 4 or 5. This could be a welcomed development to soapstone sculptors, but it is still experimental, as others have reported that the firing of soapstone has caused the destruction of a finished piece.
Appreciations
Thanks to sculptor Rich Baker of Ellensburg, Washington and to quarry operators John and Steve Pugh of Steatite of Southern Oregon, Inc. in Grants Pass, Oregon for sharing their knowledge and expertise of soapstone.
Ed note: Terry’s Tips are always appreciated when good fortune pushes them across the Journal’s editorial desks. That said, we’re obliged to add that some of the opinions expressed herein do not necessarily reflect the opinion of the editors, board, or general population of NWSSA. And, then again, some of them do.
As an alabaster/limestone kind of person, I find the prospect of carving marble intriguing but a bit intimidating. Would I need a different set of tools, carbide or diamond for example, to work in marble?
The first piece I ever carved was in marble. Being uninformed (ignorant, or at least uninitiated) I used a ball peen hammer, cold chisel, wood rasp, metal file, and wet & dry sandpaper. I am still pleased with the result. Many of the tools you now use in softer stone are also usable in marble. Admittedly there are softer marbles and harder marbles but steel tools are often quite satisfactory, especially points, claws, and chisels, in both hand and air hammer carving. Because of its brittleness, carbide tips on those tools are ground to a blunter cutting edge and must be held at a steeper angle to the stone surface than steel tools. I prefer the feel of the cutting action of the sharper steel edges in marble, but this is only a personal preference not a commandment. You will probably learn to use the point and claw closer to the final surface than you may have in alabaster since most marble won't bruise as easily as alabaster.
Steel rasps, rifflers and files are also very serviceable although they will wear a bit faster than carbide or diamond. Even so I have a small steel file that shows little wear after several years of being used on marble. I fear breaking or losing it because I have yet to find another like it. One place I would recommend carbide or diamond is in bits for die grinders or handpieces. They cost more than steel but they last much longer. At some point you may find an angle grinder with a diamond blade very useful for roughing out. I use one at some stage of carving nearly every piece I do but often I also use a hammer and point for waste removal, not for any esthetic or philosophical reasons but because it is very rapid way to move stone. But I do like an angle grinder for sanding and polishing broad surfaces.
Work first with lighter marbles, white or gray. Black, fine-grained marbles such as Belgian black are quite brittle and best worked with abrasives. Remember too that the term "marble" covers a multitude of stone types, some of which are difficult to work even with diamond tools.
You will probably have to give up your nail files, emery boards, and various sharp thingies that are great for detail work in softer stone but don't be intimidated, or lured, by all of the specialized tools available. There is always another nifty tool out there and angle grinder envy can be insidious. On the other hand, have you seen the new tool that...
Ed: this column on alabaster was last printed in Sculpture NorthWest in the March/April, 2001 issue. Bill Laprade (say it La Prawd) lives in Seattle and is a stone sculptor and a geologist. As a past NWSSA Board Officer for four years, he helped shape the policies for many Association procedures and Symposia. Bill is graciously permitting us to reprint a few of his useful stone columns and we hope you benefit from his expertise and knowledge.
Waxy, multi-colored alabaster has been the stone of choice for artists and artisans for millennia. It not only serves as the source of beautiful sculptures, but historically it has provided utilitarian objects such as jars and casks. It was prized by the Assyrians and the Egyptians for its beauty. One of its most handsome and unique characteristics is its ability to pass light; imagine, a stone through which light can be seen. While we sculptors use it for carving, alabaster's cousin, gypsum, is around us most everywhere we go and is handy on all our workshop shelves.
Geology
Alabaster is one of several forms of gypsum, and it is both a mineral and a sedimentary rock. It is hydrated calcium sulfate, CaSO4' H2O that is found in many places throughout the world. It is a sedimentary evaporated deposit that precipitates from the evaporation of saline water. The ideal conditions for its formation are (1) a restricted arm of the sea, (2) intense evaporation, (3) replenishment by normal sea water and (4) gradual sinking of the basin.
It is unknown whether gypsum is deposited directly in its hydrated form or if it evolves from other minerals. Gypsum may be transformed from anhydrite (CaSO4), as this anhydrous version takes on water when exposed to the elements near the earth's surface. In support of this hypothesis, gypsum is only found in the upper 100 to 300 feet of the earth’s crust, where the weathering process has affected the rock. Alabaster is the massive, fine-grained crystalline variety of gypsum. Other rocks that are commonly found in association with gypsum deposits are halite (salt), calcite, dolomite, clay and limonite.
Alabaster has a hardness of 2. It comes in a wide range of colors: white, translucent, gray, yellow, brown, orange, pink, green, raspberry, strawberry and variegated shades. The colors are the results of impurities such as organics, clay and iron oxide (rust), among others. Green alabaster may take its coloring from smectite clay that is commonly found in the same depositional environment. Commercially mined alabaster is bedded, with strata ranging from 3 to more than 100 feet thick. Products for which gypsum is used are fertilizer, concrete additive to retard setting time, a yeast growing nutrient, a flux for pottery, plaster of Paris, patching compounds, stucco and drywall.
Some of the locales where alabaster is found in the world are Utah, Colorado, California, Arizona, New Mexico, Florida, Tuscany (Italy), Iran and Pakistan. Much of the alabaster that finds its way to the Pacific Northwest is from Utah and Colorado.
Quarrying
Most of the alabaster quarried in southern Utah is very close to the ground surface. Only a few inches to a few feet of overburden are removed by a bulldozer to expose the stone. Because of the high elevation and rough winters, the work is carried out during long work days for about five months in the summer. The quarry areas are normally inaccessible during the winter.
Deposits of alabaster in southern Utah are layered in strata ranging from a few inches to four feet thick. In some quarries the stone breaks out in round or oval boulders that average two to three feet in diameter. The most common methods of removing the stone are a bulldozer and the use of a hand-held drill. The drill holes are closely spaced and then shims and wedges are used to break the stone into desired sizes. At some quarries, light blasting is used to loosen the stone. Experienced quarry operators check the stone for inclusions and fractures before breaking it into smaller pieces and displaying it for sale.
Working Alabaster
Alabaster is well known as a stone for teaching, because it is soft, carves easily with hand tools, and if you are fortunate, does not contain big surprises. The hardness (or softness) of 2 is conducive to easy removal of stock and yet alabaster has the ability to hold detail in the manner of many harder stones. Unlike another soft stone, soapstone, that commonly changes hardness, has hidden fractures and spalls unexpectedly; alabaster is generally uniform in hardness and contains fewer veins or fractures. Some of the flaws that do arise are veins or voids filled with clay. Fortunately these mud veins or pockets are not laterally continuous, so that although the design of a sculpture piece may have to be altered, it is uncommon that the stone is a loss. Unfortunately, the mud veins or pockets are not normally evident on the outside of the stone. While cracks or fractures in alabaster are not common, there has been some experience that Colorado pink may contain more hidden fractures than other varieties of this stone.
Alabaster can be worked easily with hand or power tools. Roughing of the form is accomplished with points, followed by toothed and flat chisels. Chisels bruise this stone easily, so inspect the surface vary carefully as you start to refine the piece with rasps and sandpaper. Rasps of different roughness or die grinders (with a jet of water to keep the dust down) are then used to impart the details of the piece. The degree to which sanding is taken is a personal decision of the artist. Some prefer to stop at 600 grit, which gives a "soft" finish, whereas others go to 1200 or 1800 grit, which imparts a bright polish. Akemi polishing fluid (stone sealer) #10-2012 or floor wax can also be used to bring out an even brighter sheen. At least three rounds of wax-and-polish are necessary to bring out a good shine.
Because of its softness and susceptibility to the natural elements, alabaster is an indoor stone. Left out-doors, moisture and freeze-thaw would soon soften the surface of the stone and ruin any details in a few years. This may be one of the reasons that the price of an alabaster piece is limited, in comparison with the harder stones.
And remember!! Keep your goggles and masks on. The dust is very fine grained and keep in mind that it is the same mineral that is used to make plaster of Paris, spackling compound and other quick-setting fillers. Don't let it set up in your body.
Appreciation:
Artists Meredith Earls of Seattle and the late Neil Gemmill of Kirkland generously shared their knowledge and expertise of alabaster with us. Thanks to Evelyn Dettamanti of Cedar Memorials and South-west Stone of Cedar City, Utah for information regarding the mining of alabaster in southern Utah.