Glass Fusing

In this post, I’ll talk about glass and a few topics in the subject of what’s called “warm glass”.

A ring I made with dichroic (two color) glass and transparent blue glass

Two pieces of dichroic glass, photographed on a black background and with a lit background

It can be very daunting, but it’s fun and people love to ask questions about it because it’s so unique.

There are a few types of glass. I don’t know a lot of specifics about the properties of various glass, but there’s window glass for houses and tempered glass (used in car windows). There’s also stained glass and fusible glass. Fusible glass “fuses” together predictably when heated and I think it’s generally more tolerant of high heat. Dichroic glass (two color) is a type of fusible glass that looks different based on lighting. Fusible glass can also be opaque, opalescent (mostly opaque), iridescent, or transparent. Fusible glass comes in two types: COE (coefficient of expansion) 96 and COE 90. COE is a scientific measure of how much the glass expands while heating. It’s important to know which COE your glass is. The two will fuse together, but there will be faults in the piece and it could eventually crack or separate. People usually pick one or the other to use in their art. I normally use COE 90. Available stock for each COE (colors and transparencies) is usually pretty similar. I think there are a couple of manufacturers that do the same glass in both COEs, but in general a company called Bullseye does 90 and Oceanside (previously Spectrum) does 96.

It’s hard sometimes to find glass supplies locally, especially for warm glass. Hobby Lobby has the most actual glass stock (it might be just stained glass) and tools that I’ve found. Michaels has stuff mostly for mosaics, but they also have a couple of basic tools like cutters and running pliers. Some regions might have a local glass shop. We had one in the twin cities that was great but closed a few years ago. It’s unfortunate not to have one nearby because shipping can get expensive for glass and heavy items like fire brick, and you always worry about shipping fragile things.

Online, I get glass supplies from Delphi Glass. They have an excellent selection of products that includes more than just glass supplies (they also have precious metal clay, jewelry findings, and more). They also have a superb information collection with videos and articles all about glass. Thankfully, since I make small things, shipping has never been a problem.

I’ll now explain some of the things you’ll need to make fused glass items.

– Pieces of glass or “frit” (kind of like grains) – frit is used in molds and melts into one piece whereas bigger pieces can be used alone.

– A kiln (my mom is an art teacher and very generously gave me one of hers). It’s kind of like this one but I’m not 100% sure it’s that exact one.

– Fire bricks to put beneath the kiln for air to flow under it

– I don’t know why, but I put a cookie sheet under everything. It could be just to protect the table surface from scratching.

– Shelf and risers to put your glass pieces on inside the kiln

– Optional mold

– Kiln paper or shelf wash to put on the shelf or on the molds so things don’t stick – kiln paper is a neat substance that turns into powder in high heat. For molds you have to use shelf wash.

– Optional glue to hold pieces together while firing (I haven’t used this but I believe it burns off, so it’s technically temporary glue)

– Rubbing alcohol to clean the glass

– Safety glasses both for cutting glass and for opening the kiln when it’s hot

– Heat gloves for handling the cover

– Optional rotary tool with a glass grinding bit (to be discussed later)

– Glass cutter or nipper

Generally, when making a glass thing (cabochon) with pieces (i.e not frit), you put 1-3 layers of colored glass and then 1 layer of clear on top. 4 layers in total is kinda pushing it. It just makes things more likely to go wrong. Also, glass always wants to be 1/4″ thick, and 4 layers has a long way to go to meet that thickness (each piece is usually around 1/8″ thick).

Once you get everything cut and assembled, you put it on the shelf and get to firing.

I recommend reading a lot about firing mainly because I’m not an expert and I would feel bad if you only took my advice. Also, there are a few differing ideas about firing schedules and you should do what you want.

Starting out, I let it heat slowly. It should go about 100 degrees F every 15 minutes which is like 33 degrees every 5 minutes. Then when you get to 1000 (so this will take at least 2.5 hours) it can go faster up to 1450 or whatever you decide for the top temperature. Higher temps provide more blobby pieces. Just like glass wants to be 1/4″, it also wants to be round, and at higher temps it’ll get closer to those properties. Then, what I do is turn off the heat, take the top off for like 3 minutes until the pieces aren’t glowing red anymore, put the cover back on, and then let it cool down on its own, which takes several more hours. It’s a very long process to do a glass firing. When it gets heated or cooled too fast, it will crack or get cloudy, so it’s best to take your time. It’s also very temperamental in mid-range temperatures so it shouldn’t be disturbed at all during that time (a few hundred to 1000 degrees)

There’s a common problem with firing called devitrification, where glass turns cloudy. I haven’t ever had that problem, I think because I let everything heat and cool slowly. A problem I do have a lot is where the “foil” from dichroic glass floats to the top or it leaks out of the side and creates a weird edge. I finally came up with a solution to this, which is to grind it off with a rotary tool. Then I fire it again at a lower temperature that just smoothes out the ground parts.

Finished pieces can be glued onto bails or rings. It’s a fun craft but very highly specialized and not for the faint of heart!