[Enamel Bits] Enameling Wizards

I am very excited by the knowledge and that is being
shared in this forum on enameling. I teach enameling in Houston and
have been enameling since 1970. I have a recurring problem that we
are encountering when doing cloisonne and I would appreciate any
ideas on the cure or cause. You can contact me through orchid or off
line. Here goes-- when enameling on a 18 or 20 ga silver base, one
coat of enamel is fired on the front of the piece (after normal
counterenameling )…perhaps a flux or light base color. We are then
imbedding gold sheet on the layer in a pattern, firing that layer in
place and then applying enamels around this metal. The final product
has a finished surface that is enamel and polished gold
metal…similar to Bill Harpers look. The problem is , we are getting
sheer fractures around the imbedded metals. Sometimes they don’t show
up for days after the piece has been finished. The metal we have been
fusing in is 22 ga 22kt gold. The sharp corners have been rounded off
so we don’t think that is an issue. Over 10 pieces have been done and
there is some sheering on most of them. The pieces are slightly
domed…enought to reflect light better, but not a high dome. The
size of these pieces is about 2-3 inches by 3/4 to 1 inch wide–a
longist rectangle. Would 24 kt work better or a different gauge ???Did
anyone take a Harper workshop and have any that was
addressed on this issue? I took one of the last workshops he gave in
the early 1990’s but this was not covered. We enamelists are so
helpful, I know some one will come up with a few hints. Also , Thanks
to Sandie Bradshaw and Diane Almeyda for their input on pierced
plique-a-jour. Thank you in advance Jan Harrell

Jan Harrell G’day Jan; I refer to your post in Orchid. Whilst I
know very little about enamelling I used to do a good deal of
scientific apparatus glassblowing, and I would suggest that in view of
my experiences your problem is due to the difference in the innate
coefficient of expansion between the glasses (enamels) and the metals
used. I would suggest that although the problem might not be
entirely cured by very careful annealing when the job is completed, it
would help enormously. If you use an annealing lehr the temperature
should be reduced extremely slowly. If you don’t have such a furnace,
I suggest that you put your work IMMEDIATELY after completion and
whilst still almost at the melting temperature of the enamels, just
inside the edge of the furnace and move it away every few minutes.
Also, remember that the thinner the wires, the fewer problems with
expansion differences.

For making copper-to-Pyrex seals (called Housekeeper seals in the
science world) we had to beat the copper out to extremely thin
thickness, and also for tungsten/glass seals we had to use several
different glasses - one on the other, each of slightly different
expansion coefficients to make up for large differences. Any use to
you? But cheers anyway, -

John Burgess; @John_Burgess2 of Mapua Nelson NZ

I, too, have had similar cracking problems when incorporating metal
elements into my cloisonne designs. I have done a few pieces which
had square wires used in place of some of the cloisonne wire. The
glass cracked in a few places around the square wire. I assume this
has something to do with the difference between the cooling rate of
the glass and the metal. I eliminated this problem by adding another
coat of counter enamel and by cooling the piece very slowly. Instead
of the usual enameling rack for firing, I placed the piece on a
honeycomb block which stayed warm a long time. Upon taking it out of
the kiln, I placed the block on top of the kiln which stayed hot. It
was often at least 20 - 30 minutes before I could touch it. This
seemed to help. I don’t know how big the metal elements are in your
design and if this would help, but it may be worth a try.–Vicki