Model for a larger public sculpture I am working on in the Bay Area. Scale is 1"=10'. Materials of the model are serpentinite and pure silver. But the larger sculpture will just be steel in the ground.
(Photo credit: Clemens Kois for Fisher Parrish Gallery).
Step 1: Quarrying Serpentinite
Serpentinite is an ultramafic rock, meaning it is from the mantle and has a high magnesium and iron content. Ma (magnesium) and fic (ferric, iron). These metals give serpentinite its green color. It is the state rock of California, although some people want to change that because it has a high asbestos content. For that reason I was cautious when I dug it up and worked with it. Serpentinite is in abundance in California because ultramafic rocks intrude the lithosphere when plate subduction occurs.
You can't buy serpentinite from a stone yard, so I had to go out and get some from nature. I looked at various geologic maps and located some outcropping near me. I went into the hills with a hammer and a chisel and picked up as much as I could. Definitely illegal, probably dangerous.
Step 2: Cutting the Stone
I wanted to use stones with some polished edges and some rough edges, so I needed to get me a rock that could do both. After careful inspection and selection I determined what stone I needed and started cutting. I used a few methods. First I drilled a few holes and then used a chisel to break off a rough chunk of stone. Then I used an angle grinder with a diamond cutting wheel (not pictured, sorry) and a die grinder (pictured) to cut the straight edges of the block and then cut the block into the two halves shown in the final piece. I used water when cutting and grinding because I was really trying to cut down as much dust as possible, being that serpentinite has a high asbestos content. That being said, I wore a respirator and always spent hours cleaning up dust and residue at the end of each work session.
Step 3: Grinding and Polishing the Stone
I needed the two touching faces of the stones to be extremely flat against one another, so first I tried to knock off any big chunks with chisels and the die grinder and then for the rest I created a flat surface and using sandpaper I polished up from 60 to 2000. 60, 80, 100, 220, 320, 400, 600, 1000, 2000, 4000. (wet sand paper!)
Varied the scratch pattern, made sure to thoroughly rinse any residue in between ascending grits.
In addition to the two touching surfaces, the front sides of each stone were also finished in this manner.
Pretty slow process, took a few days. Not many photos, but I expect everyone knows how to sand! Pictured are before and after.
Step 4: Casting the Silver
I procured about 4 ounces of silver.
Using fire bricks and a solder board I built a little furnace. Then I used one MAPP gas torch and another MAPP/OXY torch to blast the silver with heat in a small crucible. This really used up a lot of gas, like 3 bottles of MAPP and 3 bottles of Oxygen. In retrospect, I could've just used my Oxy/Acetylene set up, but I couldn't find the right size tips, and I am glad I didn't use the nicer stuff anyway because after being lit for over 30 minutes, shoved inside the little furnace, the cheapo tip on the MAPP/OXY torch was pretty cooked.
No flux was necessary.
Once the silver was liquid I poured it into my mold, which was a little typewriter tin that I leveled to make sure the casting had a consistent thickness throughout.
Then I annealed it a bit.
Step 5: Cutting and Polishing the Silver
I drew a dovetail shape on my cast silver ingot. Then I cut it out using a hacksaw, not pictured.
Then I set out on filing and polishing it. For flattening the faces I made a little fixture to hold the piece down while I filed it. For polishing, I just worked up from 100-6000. And finally a buffing wheel with some jeweler's rouge added. This resulted in a mirror-like finish.
Step 6: Fitting the Dovetail
I unfortunately didn't really document the carving process because performing the task required all my focus. Serpentinite is a really crumbly and flakey rock, but surprisingly hard, so I had to be very careful to not break off any chunks.
I can tell you that I used a die grinder to rough out the shape in the top faces of the stones, and then used a series of small chisels, rasps, files, and sanding tools to work out the final shape. Remove a little material, check the fit up, until it fits.
And that's it!