Robb: To eliminate air bubbles <plique-'a-jour> there are a couple of
ways. I use a vacumm kiln. No air, no bubbles. However, the best way
for most people is to lay in much thinner layers of enamel in the first
place. Only a couple of grains thickness at a time. Otherwise you are
just trapping air between the grains. The bubbles make the enamel look a
bit cloudy.
The clearest enamels are created with 80-60 grit. Use a screen to get rid
of the fines. But will need maybe 4-5 fillings and firings to build it up
to the thickness you need. If under magnification you have a bubble, just
grind a hole, fill with a finer grit enamel of the same color and re-fire.
Holes are not good in plique-'a-jour as they lessen the strength of the
enamel. Try using a small diamond point drill with lots of water and
grind into the hole area to break it open, clean thoroughly, using
distilled water in a ultrasonic if available. What you need to get rid of
is the sawdust created during the drilling. Now just fire a touch, to
smooth it out. Then you can rebuild the surface and fire again. I am not
sure of lead free enamels, but suspect that isn’t the problem. I just
quit using them as I didn’t like the color. Other than that they always
worked well.
Pat