Glass clay is fairly new on the clay scene. Like metal clay, it can be molded and/or sculpted and, after drying and being fired in a kiln, it undergoes a seemingly magical transformation. But instead of textured, sculpted or molded solid metal, glass clay transforms into textured, sculpted or molded solid glass! Easy to use and inexpensive, it comes in powdered form in a wide range of colors (opaque only). You can use your glass clay cabochons as you would use any fused glass cabs, such as in the hinged bracelet project or the mixed media bracelet.
Author and photos except those noted: Paula Radke
Editors: Jeannette Froese LeBlanc, Margaret Schindel and Ann Davis
Photos 1-3: Ann Davis
Experience Level: Beginner
Project Materials and Supplies
Glass clay powder (e.g., GlasClay™), two or more colors
Small dichroic glass cabochon (optional)
Tools, Supplies and Equipment
N95 or N100 NIOSH-approved particulate respirator
Container with an airtight lid, such as a jar, for mixing and storing clay
1-tablespoon (1.5-centiliter) measuring spoon
Disposable plastic spoon or wood craft stick (for mixing clay)
Plastic wrap (the thickest/strongest brand you can find)
Clay roller or rolling pin
Spray bottle (filled with water)
Silicone mold (commercial or make your own from two-part silicone molding compound)
Bamboo or wood skewer
Clean needle tool
Clean clay sculpting tools (optional)
Food dehydrator (optional)
Drywall sanding screen (aka drywall sanding mesh)
Thin ceramic fiber kiln shelf paper (e.g., Bullseye ThinFire Shelf Paper) or kiln wash and a sprayer, Japanese haik brush or wide foam brush
Kiln with digital controller
Baroque Art Gilders Paste (optional)
Prepare the clay. Although there are no toxic ingredients in glass clay powder, avoid breathing in the glass particles by wearing a NIOSH-approved N95 or N100 particulate respirator while preparing the clay. To prepare the first color, pour 2 ounces of the glass clay powder into your container and mix in 1 tablespoon (1.5 centiliters) of water , mashing the moisture into the dry powder thoroughly. (Measure both ingredients carefully: if you use too much water, the clay can stick to the mold and/or not reproduce the details well.) Add more water a little at a time, mixing it in well after each addition, just until the mixture starts to stick together. Wet your hands so the clay won’t stick to them, then gather the mixture, form it into a compact ball  and knead in the moisture thoroughly. (If the mixture crumbles while you are kneading it, gather it into a ball and knead in a little more water.) Flatten the ball into a patty. Cover your work surface with a sheet of plastic wrap, place the glass clay patty on it and top it with another sheet of plastic wrap. Roll out the clay into a thin sheet inside the plastic will help force the water further into the glass clay powder to distribute it evenly and allow it to absorb better . Peel back the top sheet of plastic, wet your hands again, gather up the clay and roll it firmly into a compact ball. Knead it briefly; the clay should feel like slightly grainy putty. If it still is too dry (and only in that case), roll it out between plastic again, pull back the top sheet of plastic, spray the surface very lightly with water, gather it up and knead it, and roll it out again between plastic. Use as little water as possible to achieve the slightly grainy putty consistency; too much water will result in a sticky mess and the clay will not hold its shape when molded or sculpted. Store the unused clay in the mixing container with the airtight lid. Prepare the additional color(s) of clay in the same manner. (For the cabochon in the photos, I used blue and yellow glass clays.) Please check specific mixing and firing instructions from your glass clay manufacturer.
Note: The prepared clay will remain usable for months if stored in an airtight container. If any mold spots develop, just remove them; they will not affect the rest of the clay.
Mold the first color of clay. When choosing a silicone mold for you cabs, plan for a shrink age rate of 15%-25%. Do not use any mold release; it isn’t needed and it will prevent the glass clay from picking up the details well. Pinch off a small piece of one color of the clay (I’m using blue here) and pack the clay into the areas of the mold where you want that color . If any of the clay gets into areas that you want to fill with a different color, use a bamboo or wood skewer to remove it.
Add the other color(s) of clay. Moisten the clay in the mold with a wet fingertip and pack the next color of clay into the mold (I used yellow). The water will help the pieces of wet glass clay bond together. If the original clay has dried, brush or spray the surface with water and allow the surface of the dry glass clay to absorb the moisture, then wet your fingertip and moisten the surface before packing in the next color of clay. Alternatively you can glue the pieces together with glass clay slip, made by mixing water into a small lump of prepared glass clay a little at a time until the mixture has a consistency similar to white craft glue. After you have packed each section of the mold with the desired colors of glass clay, moisten the last layer with a wet fingertip and add another thin layer to cover the back of the mold smoothly, evenly and completely .
Unmold the cabochon. As soon as you have finished packing the mold with glass clay, turn the mold over and gently pull the edges away from the molded clay . The glass cabochon should fall out without much effort and the clay should have reproduced the mold’s details well. If the cab doesn’t come out easily (or if the details aren’t sharp), the glass clay may have been mixed too wet Glass clay will not come out of the mold if it is too wet.
Clean up the edges and add optional details. Use a needle tool to clean up the edges or remove stray bits of a particular color that landed in the wrong place. You may add holes and other details with the needle tool and/or clay sculpting tools, if you wish , and/or embed a small dichroic glass cabochon into the still-wet glass clay with your fingertip .
Make additional cabs, if desired, and some test pieces. Repeat Steps 2-5 to make as many additional cabochons as desired. Also make a few simple test cabs (don’t bother fiddling with multiple colors for these pieces).
Dry and refine the glass clay cabochons. Air-dry the glass clay cabochons naturally or, to speed up the drying, place them into a food dehydrator or an oven preheated to 200° F (93°C) for an hour and turn them over after 30 minutes so that both sides dry thoroughly. When the glass clay cabochons are completely dry they will be very hard and can be sanded with drywall sanding screen  and/or carved as desired.
Do a test-firing to determine your optimal firing schedule. Geographic elevation, the thickness of the pieces, and the unique idiosyncrasies of your particular kiln and digital controller can affect the firing results, so always fire at least one test piece before you fire your “real” cabochons. Fire a test piece according to Step 8, and record your firing schedule and results. If necessary, do additional test firings with additional unfired test pieces, adjusting the firing time and/or temperature incrementally to find the optimal schedule for your kiln, controller and environment.
Fire and anneal the cabochons. Put a piece of thin ceramic fiber kiln shelf paper (e.g., Bullseye Thinfire Shelf Paper) on the kiln shelf or use a kiln shelf to which kiln wash has been applied (with a sprayer, haik brush or wide foam brush). Space the cabochons apart on the prepared kiln shelf . (Tip: Glass clay beads and other shapes without a flat side should be nested in fiber blanket for support before firing.) Ramp the kiln at 500ºF Unplug the vent/peep hole (if your kiln has one) or crack the kiln door slightly and look inside kiln for just a second or two. Shut the door again as soon as you can so that the interior temperature doesn’t drop. If the surface of the glass is shiny, shut off the kiln and anneal and anneal the cabs according to the glass clay manufacturer’s annealing schedule. (Annealing means cooling the glass slowly and holding it in the annealing temperature range to relieve some of the stress in the glass and avoid thermal shock. Small pieces of glass require only short annealing periods.) Cool the kiln to 100ºF (38ºC) before opening it.
Note: If you want the glass to be shinier, you can continue to hold it at the target temperature for up to an additional 15 minutes before annealing it, but there will be a trade-off: while longer hold times can give glass a higher gloss, they also can cause some of the molded details to be diminished as the glass softens.
(Optional): Add Gilders Paste highlights. Rubbing Gilders Paste into selected areas of your design and buffing it with a cotton swab is great for highlighting the details on your molded glass cabochons. When working with Gilders Paste, follow the manufacturer’s recommended health and safety precautions: avoid prolonged skin contact (you can wear latex or rubber gloves), avoid breathing the vapors from the paste and use only in a well-ventilated area.
Geneva Perkins, GlasClay™ Basics! The Book (West of The Moon Publications, 2011)
Art Glass Clay glass clay is available from www.paularadke.com