I use mid-fire, cone 6, porcelain and stoneware in my jewelry. I add mason stains to color the porcelain and use a Japanese technique called nerikomi to form layered or marbled forms. I’ll go into more detail on this process another time. Once the shapes are cut from soft leather hard slabs, I dry them between two pieces of drywall. The drywall helps keep them flat and lets them dry more evenly. I have found the edges of my shapes are more crisp cutting leather hard slabs, rather than cutting them as soon as they are rolled. I use a drill to make the holes somewhere between medium and hard leather hard. You can drill them bone-dry, but there is more risk they will crack at this stage. When making beads, I place them is a tin so they don't dry out too fast. Cracking at the hole is an issue with the beads and I haven't found a good way to solve it. I make enough to account for losing about 10%.
When the pieces are bone-dry I sand them to the thickness I want. I use a caliper to make sure all the pieces I am sanding end up the same thickness. So far, I don’t have a specific thickness I try to match. I usually pick the thinnest piece from the batch and use its thickness after sanding to gauge the rest. They usually end up a bit thicker than I like after firing, so I think I need to come up with a consistent measurement to get to the finished thickness I’m looking for.
Since these pieces don’t get glazed, I can just throw them in an unglazed bowl and fire them to cone 6. No bisque firing required. On my last batch of jewelry, I decided to skip the dry sanding all together. It requires wearing a mask and is rather dirty in general. Lots of fine dust to clean up before you can move on to something else. I bought a diamond sanding disk thinking I could just wet sand the fired pieces. Even though it is less messy and doesn’t require a mask, it took much, much longer to sand the vitrified pieces than the bone-dry ones. So back to bone-dry sanding for me.
Once they are fired, they get tumbled. The tumbling takes time, but it’s not actual work for me. Since I usually don’t have enough pieces in a batch to completely fill a 3 pound rock tumbler, I have fired random porcelain shapes to fill the tumbler. These wear down, just like the jewelry, and have to be replaced with new every so often. The tumbling process uses silicon carbide grit to wear down the sharp edges from the pieces.
There are several sizes of grit used to get the surface finish I am looking for. For matte surfaces, I only use two sizes of grit. I tumble with the most coarse grit for two weeks. This will take off the sharp corners and give the pieces nice rounded edges. You have to check the tumbler every few days to make sure pieces don’t get stuck to the bottom of the tumbler. When they get stuck, you end up with one rounded side and one very sharp side on the edge. It’s not very attractive. Once everything is nice and rounded, the coarse grit is cleaned out and they are tumbled with a finer grit for a week. This surface is very soft and smooth, but not shiny.
You can shine the pieces to a high gloss, but it takes more time. One week of tumbling with a very fine grit and a final week of polishing. The nice thing about polishing, rather than glazing, is the shine is on the surface of the colored porcelain. There is not a layer of clear glass between the shiny surface and the ceramic.
Now the pieces are ready to make into jewelry! I mostly make earrings, but I have made necklaces also. Hop over to the shop to see what is available!