Melting Glass in Ceramics

Once upon a time when I was in high school, my friend and I who had both decided to major in art education, were given a lot of freedom to experiment in art class. Somehow one of us came up with the idea of sticking stained glass scraps into clay and melting it in the kiln. We made some very colorful coasters and I remembered loving to see how the colors looked after being fired. I also have a nice scar on my thumb from the experience, but that's another story.

Last fall my boot camps covered mostly 2D media and while I was planning to wait until January to start introducing clay, I had a weird gap at the end of the semester and figured that a clay tile project would take just the right amount of time. I showed students several techniques they could try, but almost everyone got excited about the prospect of melting glass in carved out tiles. Many made projects for Christmas presents or since I finally gave them a chance to make something with the logo of their favorite team or brand to get it out of their systems, something just for fun.

We used the slab roller we received through Donors Choose to roll out slabs about 1/2 inch thick. Many students had their plans on paper and used a needle tool to transfer the drawing onto the clay, marking the edges and where clay would be carved out to make a well for the glass. We aimed to have the carved out areas about half the depth of the slab and to keep the bottom level. Some students carved too deep and were able to patch the bottom with fresh clay. When the carving was complete, (easiest if the clay has set up for a day or two but most of us just went for it after the drawings were transferred) we let the clay dry out and then tried to remove any "crumbs". I bisque fired to cone 05 when the tiles were bone dry.

 When the tiles were out of the first fire, students glazed the sides and the flat part of the tile, leaving the carved out sections unglazed. The glass basically serves as glaze for those areas. After glazing, we filled in the carved sections with small pieces of glass.

Here are some things I learned about this step:

1. Small pieces are easiest to arrange and to get into all the little corners.
2. We used a hammer, a piece of felt, a rock, and safety goggles when breaking up the glass. Fold the felt in half with the glass in the middle. Place the felt on top of the rock, and while wearing safety goggles, use the hammer to break the glass.
3. Plastic baby food containers work well to store and sort the broken glass. Just label with a sharpie and find a storage container to hold the smaller canisters.
4. You can use aloe vera gel to stick small pieces of glass in points or sections where they tend to slide. The gel holds the glass in place and burns out in the firing process with no weird film or anything left behind.
5. Glass is unpredictable. Some glass colors get darker when fired- many reds turn out brown, gold turns orange, etc. Some colors, like the purple I bought, kind of bubble out of the edges. One green glass turned out like rock candy instead of melting smoothly at cone 05. It just depends on what kind of glass you have. I'm hoping to get some more stained glass and make samples with each color so students can see how it changes in the kiln.
6. If you end up with a funny broken air bubble after the first firing, or did not fill in with enough glass, you can add more glass and fire again. We aim for putting in enough glass to be level with the top of the tile.
7. Some colors will swirl together if you put them in the same section and some will not- it usually looks cool either way.
8. It is super important to make sure that your glass filled tiles are sitting level in the kiln for firing or the glass will run out of the carved areas.
9. If you are out of one color of glass, you can glaze that area and put clear glass on top. I had a bunch of those flat glass marbles that cost about a penny each and we melted them on top of a glaze when we briefly ran out of red.

You can see that some of the glass in this tile created a funny texture on the surface, but the other colors all melted fine.

Because I knew the purple would bubble out, I suggested this student use a dark glaze around the powercat (getting that favorite team logo out of his system) and it solved the problem.

Last week a student asked about putting glass on a mug. I'd never tried it on a round surface before but since it wasn't going to be a big area, we decided to try it. Since it wasn't a big area, I was able to use kiln stilts to lay the mug on its side and point the heart up so the glass wouldn't run out of the carved heart. I look forward to experimenting more with this technique!