The expansion rates (COE’) have all been determined for you and are
listed in the workbook on pages 3 & 4. for each enamel. They also
list the fusion flow, and dilatometic softening point. However, the
important numbers for enamelists are the expansion rates. People
working with glass need to be aware of the softening points and
The numbers listed in the Thompson workbook are for the lead free
enamels. For the old discontinued lead bearing enamels, you will have
to ask Thompson to send you the chart with that
As I do a lot of layering of transparent enamels in order to achieve
certain effects,I find that it is essential to know the COE, so that
I will not be putting one with a high expansion over one with a low
expansion as to do so, invariably results in cracking, and even
popping off. Sometimes this will happen days after one has completed
Also, when I am working with colors having a high expansion rate, I
make sure that I am putting them over a flux that has an even higher
rate of expansion.
Regarding hard and soft enamels. This is indicated for each
flux–hard, medium, soft.so you don’t have to do any research on
that. Regarding the various colored enamels. Fortunately almost all
of the enamels fuse at the same temperature and length of time. So
you don’t have to concern yourself too much about it. There are a few
exceptions—one being the old lead bearing Amber. It takes longer to
fuse, so, when I use it on a piece that has a number of other colors,
I put the amber on early in the enameling process so that it fully
fuses, then work with the other colors.
Reds are notorious for burning out (turn ugly brown, or blackish).
These go on for the last firing.
Much of my work consists of commissioned large wall enamels. I can’t
afford to take a chance with these and have to be very careful about
the COE, and other factors.
I am just as careful with small jewelry items, as nothing is more
disappointing than putting in hours of work on a special cloisonne
enamel, only to find hairline cracks appearing just when one is
nearing completion of the piece.
If you run into any special problems or have questions not answered
in the Workbook, give Tom Ellis, or Bill Helwig at Thompson enamel a
call. They are the experts, and are always willing to answer