A pendant made in a microwave kiln.
Blue glass sprinkled with dichroic glass.
It is difficult to believe that the microwave
ovens we use to heat soup and bake potatoes can get hot enough to fuse or melt
glass. In reality, not only can microwave ovens fuse glass, but most ovens can
do it in less than 10 minutes.
I first began experimenting with microwave
firing last year to make glass-fused pendants. I used the microwave oven in the
Paragon employee kitchen for most of the firings, and I also used two smaller
and inexpensive microwaves to compare the results I was getting with the larger
Making glass jewelry is fun and will teach
you the principles of glass fusing. With practice, you should be able to
achieve consistent results in microwave firing. You will need a microwave kiln,
which is a small ceramic fiber container that fits inside the microwave oven.
The microwave kiln captures microwave energy and concentrates it in the firing
chamber. The concept is similar to using a magnifying glass to focus sunlight.
The biggest challenge to microwave firing is the fast heating rate. A microwave
kiln reaches 1650°F (899°C) in only 5-10 minutes. Firing times depend on the
wattage of the microwave oven; the lower the wattage, the longer the firing
time. However, firings can be controlled to achieve consistent results.
Only small glass projects can withstand rapid heating. The glass should be no
larger than 1 x 1½ in. and no thicker than two layers of 1/8-in.
stained glass. The glass must be clean; even a greasy fingerprint can cause the
glass to break apart during the initial heating.
Figure 1a. Place the bottom of the kiln on top of
three ½-in. ceramic posts.
Though these instructions are basic, more
detailed information will be included in your microwave kiln manual. Fire only
fusing-compatible stained glass, or the pieces will break due to differences in
their coefficients of expansion. Your stained glass supplier can show you how
to cut the glass. Required supplies include a microwave oven and kiln, kiln
wash and a small paintbrush, clear firing safety glasses, heat-protective
gloves, six ½-in. kiln posts, a 12 x 12-in. kiln shelf or other heat-proof
surface, and a glass cutter.
First, protect the base of the kiln by applying a coating of kiln wash
or glass separator with a small paintbrush. The coating prevents the glass from
sticking to the kiln base. After the coating is completely dry, place the glass
pieces on the base.
Lay the 12 x 12-in. ceramic shelf or other heat-proof surface near the
microwave oven. Arrange three ½-in. ceramic posts on the shelf. When the glass
has fused, you will remove the kiln from the microwave and place the kiln on
the three posts.
Figure 1b. Position the kiln gently over the kiln base to
avoid jarring the glass.
Most microwaves have a rotator tray. If the
rotator tray in your microwave is stable, it will provide better heat
distribution within the kiln. The tray in some models vibrates or jerks,
however, which will cause stacked glass pieces to fall apart as the tray moves.
If that is the case with your microwave, remove the tray. Alternatively, a tiny
drop of Elmer’s white glue will hold glass pieces together, though the glue
does increase the chance of glass breakage.
Position the glass pieces on the kiln base. For your first firing, load
only one test piece. (Later, you can try firing three or more pieces per load.)
Place the kiln bottom and glass on top of three ½-in. posts inside the
microwave. You can place the posts on the rotator tray or directly on the
bottom of the oven if you’ve removed the rotator tray. Gently position the kiln
over the kiln base and close the microwave oven door. The loading process is
shown in Figure 1. You are ready to fire the glass.
While it is okay to fire small pieces at full power, starting with 50% power
for five minutes increases the success rate, especially with larger pieces. The
glass is less likely to break with a pre-heat. See your microwave manual for
instructions on reduced power settings. (You can probably find the instructions
on the Internet if you don’t have the manual.)
2. Lift the kiln quickly to check the progress of the glass.
After a five minute pre-heat, set the
microwave oven to 10 minutes at full power and press the start button. Wear heat-protective
gloves and clear safety glasses. After four minutes, open the door. Working at
arm’s length, lift the kiln top about ½ in. and quickly look at the glass (see
Figure 2). (Do not get close to the hot glass as you check it visually.) The
glass will probably not be fused yet. If that is the case, close the door and
press start. The microwave will continue to heat.
3. Remove the kiln immediately after the glass has fused to completion.
Keep checking the glass every minute. When it has fused just the
way you want it to, remove the kiln and base from the microwave. Gently set the
kiln on the three ½-in. posts that you placed on the ceramic shelf (see Figure
3). Do not disturb the kiln. Allow it to cool for around 45 minutes.
As you gain experience, you will sense just when to start visually checking the
glass. I check every 20 seconds toward the end of a firing because I want to
stop the firing at a precise stage of fusing, usually between tack fuse and
stages of glass fusing (from left to right): tack fuse, medium fuse and full
Once you learn how to achieve good results
consistently, you will be amazed at what you can make. I gave a glass-fused
pendant to my 13-year-old niece and she liked it so much that she even wore it
while she slept.
I learn something new every time I fire a microwave kiln. You can experiment
endlessly with designs and colors. I used hairspray as an adhesive once, and
the spray produced a beautiful silvery sheen over dichroic glass. You will make
many such serendipitous discoveries with microwave glass fusing.
For additional information
regarding glass fusing, contact Paragon Industries, L.P. at 2011 South Town
East Blvd., Mesquite, TX 75149; (972) 288-7557; fax (972) 222-0646; e-mail email@example.com; or visit www.paragonweb.com.
Please follow the safety
rules in your kiln manual, and always wear clear safety glasses when looking at
the hot glass.
SIDEBAR: Microwave Kiln Safety
- Wear clear safety glasses whenever
visually checking hot glass, and stay at arm’s length.
- Fire only fusing-compatible glass in a microwave kiln.
- Wear heat-protective gloves when removing
the hot kiln from the oven.
- Remove the kiln from the oven immediately after the firing is
completed to avoid over-heating the oven.
- Separate the hot kiln from the heatproof
surface with three ½-in.
- Allow the kiln to cool for at least 45
minutes without lifting the kiln top.
- When opening the kiln after it has cooled, lay the kiln top
upside-down on the heat-proof surface. Placing the top open-face down may cause
heat to build up within the lid.
- Keep the hot kiln away from children and pets.