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The Stone Corner

The Stone Column: Granite - May/June 1996

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 b

eauty 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, Mount Index.




One of the most fascinating features of granite is that it is comprised of so many minerals. It is that combination of the different minerals and sizes of crystals that gives granite so many appearances. The major constituents of granite are quartz, plagioclase feldspar, potassium feldspar, b

We need to make a distinction between common usage of the term granite and the geologist's version of the word. The commercial use of the word is considerably broader than the geologic use. To geologists, true granite is a very limited occurrence of the rock that contains more than 10 percent quartz, greater than 2/3 potassium feldspar, along with biotite and hornblende, and is very light in color; generally with dark specks. All of the other versions are granitic rocks that have specific names that are defmed by the percentages of the major constituents. The common lighter colored granitic rocks are quartz monzonite, granodiorite and quartz diorite and diorite, in order from light to dark. 

The very dark or black granites are diabase, gabbro, anorthosite and pyroxenite.iotite and hornblende. Quartz is 

the glassy one; the feldspars are the opaque ones; biotite is black 

mica and hornblende is the black, lathe-like mineral. Other minerals that commonly fmd their way into granitic rocks are magnetite, ihnenite, apatite, pyrite, zircon, allanite, tourmaline, olivine and muscovite.


Read more ...

The Stone Corner - Anhydrite -Sept/Oct 1997

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.



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.



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.



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.



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.



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.

The Stone Corner - Slate - July/Aug 1997

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.



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.



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.



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.



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.



Thanks to artist Ward Lynch of Everson, Washington for sharing his slate carving experiences with me.

Stone Corner - Bronze: Concept, Material and Process - May 1997 Jan/Feb 1997


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.



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.



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.



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.


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.



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.



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.

Stone Corner - Sandstone Jan/Feb 1997

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.



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.



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.



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.