FINISHING SOFT STONE
By JoAnn Duby
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.
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 to 220 grit.
• With silicone carbide paper, sanding to 320 grit, and then polishing 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.