Glass Fusing

Glass fussing is the process of combining cut pieces of glass with the same COE in a kiln.

In order to fuse glass you have to know at least some basic properties of the glass. The first thing that is the most important is that all glass is not created equal. Glass expands when heated. This expansion can & is measured. This expansion is called Coefficient of Expansion (C.O.E. - the rate at which glass expands). The glass you will fuse has to match in expansion or it will crack upon cooling. Bullseye glass, Wasser glass & Uroboros glass make tested compatible at 90 C.O.E. Spectrum System 96 & some Uroboros glass is tested at 96 C.O.E. Moretti is 104 C.O.E. & Pyrex (Borosilicate) is 32 C.O.E. Never mix glass that you don't know the C.O.E. of unless you run compatibility tests.

4 inch tile project

Prepare your kiln:

Apply kiln wash to your kiln shelve. It is best to go in 1 direction, as the brush strokes will be texture on the bottom of your piece. Wait for the layer to dry. Apply another layer at 90 degree angle from the previous application. You can wait for it to dry for a few hours or fire the kiln to 500° to evaporate the water in the kiln wash being sure to vent the kiln lid with a small kiln post. Let your kiln cool naturally.

Create your project

Materials:
a glass cutter
compatible glass 2 pieces
Elmers glue
thin it just a little with water or use honey
Windex
or Honey
Optional: Frit, Confetti, or stringers

Use glass of standard thickness (approx. 1/8 inch [3 mm] thick). It is best to start with clear plus colored glass for decoration.

1. Cut your 2 pieces of glass & clean them well, the oils from your fingers can leave ugly marks on fired glass. Lay your bottom piece down on your kiln shelf. Then lay your top piece on it.

2. Cut designs out of thin glass, and or frit, stringers, confetti, and lay them on top of your glass. You can hold them in place with a drop of the thin Elmer's or the honey. Do not pile up your decorations on top of each other, you can overlap some of the pieces but just don't pile it up.

NOTE: The taller you go the more you piece will move and melt on the shelve, the glass will always try to be 1/4" thick.

3. Fire!

FIRING

Your target temperature for a full fuse is 1450°. Tack fusing occurs around 1325°-1400°. Each kiln varies so you will need to experiment to find what is your real fusing temperature.

Firing Ramp (for small thin pieces)

900° per hour to 1000° for top fired kilns
600° per hour to 1000° side fired kilns
Ramp full speed to 1175° Hold for 12 min

This will help relax the glass and reduce air bubbles
Ramp full speed 1450°
hold for 20 min
cool down to 1000
hold for 1 hour to anneal

It is important to get past the 1300 - 1400° as quickly as possible. This is where glass will devitrify and create ugly white stuff on the surface of the glass. For smaller older kilns you might need to babysit the kiln at this point and watch it until it reaches a full fuse. You can ID a full fuse by the flatness of your piece and the rounded look to the edges.

Once your glass is 'done' pull out the peep hole plug & open the kiln lid all the way to "flash" vent your kiln. Vent until the temperature drops to 1,000°, (if you wish you can rest the glass for 5 minutes or so at 1,000° to distribute the heat evenly). then close the lid & replace the plug. If your kiln has thick fire bricks & cools slowly you can turn it off & let it cool to room temp. If it is a ceramic fiber kiln you will have to fire down at a rate not faster than 300° per hour. Typical cool down is 6 - 8 hour for all projects of up to 8 inches across & 2 to 3 layers thick. Never take you glass out of the kiln until it is actually room temperature. If you do you will thermal shock your glass by exposing it to cooler air while still brittle & hot. It might not break now, but it might break 6 months from now if you shock it.

Glass is brittle between room temp & 1,000°. Do not open your kiln under 1,000°. At over 1,000° the glass is hot enough to view it. Please wear eye protection when viewing your "hot glass". The air escaping from the kiln can damage unprotected eyes!

If you want to re-fire your glass a second time to slump it or add more decoration, remember that it is now twice as thick & you can only heat it up at 450° per hour. (heat half as fast as when you first heated it up. Cool down is the same way.)

DEFINITIONS

full fuse: To unify glass completely into one solid layer.

tack fuse: to fuse the glass while keeping the shape of the different pieces and dimensional shape of the glass.

frit : small broken up particles of glass

COE: Coefficient of expansion. Don't mix glass with different coefficient of expansion (COE). It will just break up. This is due to glass such as (Moretti 104 c.o.e.) heating and cooling at a different rate than say Bullseye which is 90 coe. The coe can be no more than 1 point in difference.

confetti : little pieces of very thin glass flakes

stringers: thin long pieces of pulled glass

noodles: what you make stringers out of.

devitrify: Surface of glass has crystallized due to remaining to long in the temperature range just before it get molten. (Some dark colored glass & some opal glass is subject to devitrification more than others. Such as transparent cobalt.

Anneal: To make harder or strengthen. You can't over anneal your glass!