Programming instructions

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Q. Do you have to re-coat the kiln shelf with primer every time you use it?
A. If the shelf primer is in good condition it can be used more than one time. The shelf should be
scraped, sanded or washed clean with clear water and re-coated when the primer shows signs of wear.
It’s time to re prime when the coating becomes thin (usually where a project rested) has cracks, or
begins to flake off.
Q. Why does kiln wash stick to the back of a project?
A. This is usually the result of exhausted kiln wash; the shelf should have been re-primed prior to use.
It may also occur when the glass has been fired to too high a temperature or kept at full fuse too long.
The kiln wash can be removed with fine steel wool or a scraping tool. Stubborn patches can be soaked
off with bathroom cleaning products used to remove hard chemical residue.
Q. After the project is fused, how close to room temperature do you have to be before opening
the kiln lid?
A. How badly do you want the project inside? Room temperature is usually well below 100 °F. If you
open the lid prematurely thermal shock can occur; breakage caused by changing temperature too fast.
Just a quick peek in to the kiln, done too early can ruin your day. Wait, it will be worth it!
Q. What causes tiny bubbles and how do I get rid of them?
A. Air becomes trapped between the layers of glass when it is heated. The number and size of the air
bubbles can be reduced by heating the glass more slowly between the temperatures of 1000 – 1465 °F.
This gives the air more time to escape before the glass edges become sealed.
Q. How do I avoid big bubbles?
A. Large dome shaped bubbles will sometimes rise up in the middle of a medium - large (4” x 4” or
bigger) projects. This is usually the result of firing too fast on a ceramic kiln shelf. The outer edges
of the project become soft first and form a “seal” on the shelf. Air becomes trapped under the glass.
When it expands it lifts the glass. This is less likely to happen when using shelf paper or a fiber board
kiln shelf, as the air can escape through the porous materials. Best advice is to slow down the firing
process.
Q. Can I stack kiln shelves?
A. Not recommended. Unlike ceramics, glass is thin and reacts to heat quickly. Stacking shelves
causes uneven heating. The outer edges of the project become molten before the center has a chance
to react; your firing results will be inconsistent.
Q. How does the thickness of the glass relate to my target temperature?
A. A project made with two layers of thin fusible glass will usually reach the desired “look” before a proj-
ect made with two layers of 1/8” glass. When you change project sizes or materials (thin vs. 1/8”) you
will want to monitor the first few firings and make any necessary adjustments to your firing schedule.
Q. Can more that one project be fired in the kiln at one time?
A. Yes, as long as the projects are similar. They should be made from the same thickness glass,
have the same number of layers and be close is size. Use a firing speed for the largest project. Small
projects will not be harmed by firing slowly but a large project will suffer if rushed.
Frequently Asked Questions
GLASS 101