Glass Decals are separated from Ceramic Decals NOT by the surfaces that they go on, but rather by the fusing and maturing temperature they have been engineered to fire at. Glass Decals use glass decorating colors which are fired to Cone 022. If a surface can withstand 1100°F, a Glass Decal will fuse there. I’ll talk about nontraditional surfaces later.
High Fire Colors – Used in Glazes and Underglazes
Low Fire Colors – Used in Overglaze Decorating
Glass Colors – Used in Glass Decorating
Now a color manufacturer can spec out a color to any temperature that you want, but generally, most colors fall into one of the above groups.
Want to know a little
Some companies have what they call “glass colors” which are sold to be used specifically for glass sagging and fusing. Guess what? They aren’t really Glass Colors. They are Overglaze Colors, which just happen to fuse and mature at the same temperatures that you fuse and sag at, namely, Cone 015-018. This is not done to deceive the public. It is just simpler to call them “Glass Colors for Fusing” rather than explain that they are Ceramic Overglaze Colors that are being used for glass combination decorating/sagging/fusing techniques.
Here are my firing instructions for firing Glass Decals on Soda Lime Glass:
• Put glass to be fired into
- “Stilting” is not necessary
- Stemware should be turned upside-down
- Never place glass closer than 2” to the kiln heating elements
- Always be sure that the kiln shelves have a sufficient coating of kiln wash
- Place pieces in the middle or bottom of the kiln. Remember, a kiln is hotter at the top.
• Set Cone for 022
• Set Firing Speed for FAST
• Leave kiln lid cracked about 1”
• Leave all “peep holes” open
> Start kiln
• When kiln stops smoking,
This will usually be about 45 minutes into the firing (with a small kiln)
“Peep holes” may remain open
• When kiln shuts off,
crack lid (1”) IMMEDIATELY
This is the most important step!
• Let kiln cool down naturally
• Remove ware when kiln has cooled
• Turn ALL switches on HIGH
• Put 022 cone into “Kiln Sitter”
• Same instructions as above
- It is not necessary to crack lid at the beginning
- Leave “peep holes” closed (except for the one in the kiln lid)
- Turn OFF the Power Vent when the kiln temperature has reached 950°F
- Turn ON the Power Vent IMMEDIATELY when the kiln turns off
Or, preferably, crack the lid 1”. Cracking the lid allows a faster cool down from the highest temperature, but still let’s everything return to room temperaturegradually
Most Glass can be grouped into one of 3 categories:
Leaded Glass – Very soft, very exquisite, very expensive.
Boro-Silicate Glass – Cooking Glass, like Pyrex. Very hard, very durable, not cheap.
Soda Lime Glass – The Everything Else Glass. Coke bottles, tumblers, ash trays, jelly jars, you-name-it. Medium hardness, dishwasher-safe, inexpensive.
Actually there are about 15 kinds of glass, like optical glass and bullet-proof glass, but I mention the top three because these are the ones most accessible to consumers and artisans. Moreover, Glass Decals, like Ceramic Decals, are fired differently depending on which glass surface you put them on.
Soda Lime Glass is decorated at Cone 022 and typically fired quickly.
Boro-Silicate Glass is fired at Cone 020-021 and fired much like ceramicware, slowly.
Leaded Glass is fired at Cone… I have no idea what cone Leaded Glass is decorated at because no one ever decorates Leaded Glass, except maybe with gold. It being a softer glass, I suspect it is fired at Below 1000°F, but who knows. (I read one person saying that she believes that Leaded Glass starts to soften at 750°F. Wow!)
Wwaaay More Than You Wanted to Know About Glass
There are several ways to fire glass for decorating. I prefer the “fast” method because you don’t need to open the kiln lid at 1000°F (Can you say s-i-n-g-e-d e-y-e-b-r-o-w-s?) The theory behind Fast Firing for glass decorating has to do with a little known phenomena called the Quartz Inversion Temperature. The Quartz Inversion Temperature is at exactly 1063°F. At this temperature everything with quartz in it does a little dance, in fact, it expands a little. When glass has passed this point, it is thinking about warping (not melting, just warping). This dance has a destabilizing effect on asymmetrical ware. Well, my half-baked theory is that if you quickly raise and lower the temperature of the glass to the maturing point of the decal, the glass doesn’t have enough time to think if it wants to bend or not. The theory has been born out in practice. I suggest that if you would like to test it, go buy some Thrift Store glass (or pull a pickle jar out of you garbage can) and try it. Frankly, once you try it and are convinced that glass decorating is easy to do, you’ll be hooked… like me.
1) You can fire CERAMIC decals on glass when you sag it… at the same time you are sagging it!
2) You can fire GLASS decals on ceramics… at cone 022!
3) You can use both CERAMIC and GLASS decals on soap and candles (aka. cold mounting).
4) If you have a “glass” kiln, you can use it for all overglaze firings, viz. gold, decals, luster’s, and china paints, as well as the 3 different glass cones. Oh, I didn’t mention the 3 glass cones? 022 for decorating (the glass holds its shape); 018 for tact fusing (the glass sticks to things); 015 for sagging and full fusing (the glass melts and flows).
5) But except for Full Fuse Layering (which is better done in a glass kiln), everything we’re talking about can be done with a normal ceramic kiln, especially if you happen to be running a small over-flow kiln (aka. a “gold kiln”, namely, a small kiln used for specialty firings, like lusters and gold and decals, or some extra pieces that wouldn’t fit in the main kiln). Small kilns work best for glass firings.