FREQUENTLY ASKED QUESTIONS

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 degrees. 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
degrees. 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 project
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.

Q. What causes sharp edges on the project?
A. Dragging is usually caused by over firing a project that is resting on fiber paper. As the glass contracts and
draws in on itself the paper resists, sharp edges are the result. This edge can be made safe with file a or
grinder. After grinding the project can be put back in the kiln and heat until the ground edge is polished.

Q. Why is there debris between the glass layers?
A. Too much glue. Small amounts of glue will burn off leaving no trace. (See: Glue above for more info.) If
you use an excessive amount of glue it will burn becoming sealed between the layers, leaving dark blotches.
Excess glue can also cause small eruptions that will blow a hole through the glass or cause pieces to jump
and move in the kiln.

Q. What are the differences between using a ceramic kiln shelf or fiber paper?
A. Ceramic Shelf:
• Fused glass will take on the texture/ pattern of whatever it is fired on. If you fire on a ceramic kiln shelf
your project will have a smooth back surface. (Great for bowls, plates, fine art pieces; projects where
a sleek underside is desired.)
• Ceramic shelf is used over and over again.
• A ceramic shelf is dense; it retains heat which allows the glass to pass through the critical stages slowly.
• Ceramic shelves have to be primed frequently, this can be time consuming.
Fiber Paper:
• Shelf paper comes in a variety of thickness and finishes. Generally the thinner the material the
smoother the fusing surface. (Great for coasters, pins, wall art; projects where a textured back side
will make it easy to glue accessories on like rubber feet, pin backs etc.)
• The thin material can be used only once. The medium material can sometimes be reused; it leaves a
matt finish on the back of the project. The thick material can be used multiple times but the texture on
the back of the project will be course.
• The fiber paper is porous. Air can circulate, therefore large air bubbles are less likely to form between
the glass and the shelf.
• Shelf paper has to be cut to size and can be costly if you are using it every time you fire.

Q. What are the differences between ceramic molds and stainless steel forms?
A. Ceramic Molds:
• Ceramic molds come in a wide variety of sizes and shapes. They have to be primed like the ceramic
kiln shelf. The primer tends to last longer on a form than on a shelf because slumping temperatures
are lower than fusing temperatures. Slumping occurs at approximately 1200-1300 degrees.
• Ceramic molds are inexpensive and durable but they will break if dropped or used unprimed.
• Ceramic molds should be sanded and be re-primed if there are pits or cracks in the coating.
• Ceramic molds cool more slowly than the glass. Therefore most molds are shaped so the glass
slumps down into the mold, allowing the glass to contract first.

Stainless Steel Forms:
• Stainless steel forms come in a variety of shapes and sizes as well. They have to be primed also. The slick surface makes priming difficult. The form can be sanded, sandblasted or heated to make the priming process easier.
• Stainless steel forms are extremely durable “forever” molds. But they tend to be several times more expensive than ceramic molds.
• Steel forms should also be sanded and re-primed if there are pits or cracks in the coating.
• Steel cools more quickly than the glass. The metal contracts underneath the glass which gives the room needed to slide the draped piece off the form.