Recently I did an extensive sculpture project using recycled tempered glass in plaster silica molds. It’s a fascinating process with many steps.
The final sculptures are the awards for the Clear the Air Challenge 2012. But, the pieces are so cool, I predict there will be more Wasatch Mountain Range sculptures in my future.
Sculpting the original
Using a color photograph enlarged to what will be actual size, I used white ceramic clay to sculpt the Wasatch Mountain range in three dimensions. This was much more challenging than I expected. This portion of the process took nearly 16 hours. The final dimension is 15″ w and 3.5″ tall.
Finished Original
After adding a flat base to give the piece stability. Next step is making a plaster silica mold to cast the sculpture into.
Pouring the plaster silica mold
Here the original is in a cardboard box awaiting the plaster silica mix. The box is about 1.5″ larger all around than the clay original.
Using a 1:1:1 plaster/silica/water mix, the slurry is carefully poured into the box. I’ve taped across the center to keep the sides from flaring out. Moo the shop cat checks my pouring technique.
The finished plaster silica mold
After peeling out the ceramic original, the plaster mold looks great! As you can see, the same can’t be said for the clay original. Since I need a minimum of 3 of these pieces, I’m going to create a silicone copy of the mountain range that can be used to pour two more plaster silica investment molds.
Making a silicone copy
Using a handy recipe I found on Instructables, I’ve made a silicone molding compound and filled the void in the mold. There are specialized mold making compounds available, you should check your options. I like this particular solution because if I run out, I can go right over to the hardware store and get more, rather than order the specialized stuff and have to wait for it to show up.
Finished Silicone Master
The film on the surface is a result of a reaction between the plaster mold and the silicone mold making compound. It looks weird, but doesn’t affect the end result in any way. Using this master, I pour two more plaster silica molds.
Charging the molds with glass
I’ve opted to use large and small chunk tempered glass for the casting of these Wasatch Range sculptures. The glass will lose somewhere between 30 and 50% of its volume as it melts down into the molds so I’ve packed the molds as closely as I can and piled extra on top. At this point, I do this by eye, simply because I’ve done it so many times that I can. If you look you can see stainless steel wire around the outside of the mold, because I’m mildly paranoid and plaster silica molds have a tendency to crack.
Fuse!
The two molds on the left had large chunk (3/8″ thick) tempered float glass, the one on the right had small (1/8″ thick) chunk tempered glass. You can see there is a difference in clarity, the larger chunk glass gives a clearer end result. You can see that there is some mold cracking, but not too bad.
The firing schedule I used is the standard fusing schedule, but I extended the top hold to 30 minutes and adjusted the cool down to accommodate the thicker glass.
De-molding the sculptures
There’s a fair amount of cold working to be done here, particularly removing that big old fault line running down Mount Olympus. The end result is good though, always a nice thing.
As an interesting, potentially useful side note, as the silicone master cured over a course of 6-8 weeks, it shrunk quite a bit. Here is a picture of the silicone master now, next to the glass that came out of the mold made with the same master 6 weeks ago.
My next sculpture project is making re-useable ceramic casting molds of this same piece. It will be an interesting study in contrasts.