generally do not need to anneal. The bigger your pieces are, the longer you'll need to anneal. Your
firing results will give you an indication of annealing times that will work for your size pieces. For
larger pieces start with a 30 minute anneal, then you can work your way down to shorten your
schedules if you like for the smaller ones.
Many calls have come in saying that the glass must be cooled slower that we are recommending. If
glass is on a clay shelf we agree, it should be cooled at the same rate of the shelf which can be 150
to 200F per hour. But on fiber the glass can cool quicker since it is resting on a non heat absorbing
surface. In our challenges that was have received, we started taking fused glass work that was fired
quickly and once cooled put into our freezer overnight. Then the next morning took it from the
freezer to the sink and ran hot tap water over it. If it were to crack then it will need more
annealing, if not then this is a good real work test. At Jen-Ken Kilns no pieces have broken yet.
In addition to this if the fused piece is to be slumped, then the next firing will be slower since the
glass has now been fused and is thicker. The ceramic mold has to be heated slower to prevent
breakage and if annealing is still a concern it can be at the end of is this firing. Just make sure there
is a step to hold at 950°F for a while and then cool from the 950° to about 700° at 150°F per hour.
Thick Glass and Slumping
Ripple glass is thick and thin over the entire surface and will need to heat slower than two or three
layers of single strength glass to accommodate the glass variances.
Double strength glass will also need to fire a little slower (more like 500°F or less and not FULL (as
fast as possible) on the way up.
Remember, a fully fused piece of glass is now 6mm or thicker, and cannot be taken as fast as the
thinner assembled piece in any future firings. You'll need to slow it down for a second firing of
your fused work. Try using a program from the SP mode, if re-fusing the same piece or the slump
program in the SP mode if slumping glass over a ceramic mold.
Small Jewelry Sized Pieces (3” x 3” or less):
These sized pieces can be fired VERY quickly in the fiber kilns with no adverse effects. Full / to
1500°F/0 hold in the Bonnie Glo and Full/1470°F/5min hold in the Pro-Fusion 16 have been
successfully fired schedules in our studio.
The Bonnie Glo Kilns
The Bonnie Glo
is a top loading kiln where everything goes in from the top. It is a 15” x 6” deep
kiln and can handle up to a 14” diameter piece or a just about 10”x 10” square 2 layer piece of glass
to be full fused. If thick work is to be full fused it will spread out to be larger as it seeks a ¼”
thickness. It has a lid handle to open and close the lid as well as a lid prop support to vent the kiln
as needed. Some use the lid prop on the lowest setting on the way up to vent the kiln paper fumes
out of the kiln and then close it at 800°F, using a tool (Caution: Hot handles look like cold
