When you heat enamel, there are certain chemical reactions that
happen. Enamel is powdered glass, most often with metal oxides added
that produce various colors. When it is applied to an appropriate
metal and heated to between about 1350 degrees F to 1550 degrees F,
it loses its powdered quality, “melts” and fuses into a sheet of
glass.
Choosing the temperature level of the kiln to cause this reaction
depends on several factors. First, different glasses have different
co-efficients of expansion, which means they need more or less heat
to get to the fusing state. Generally, enamel manufacturers have
already taken this into account, so enamels fire at the range I
mentioned above. If you look at the Thompson enamel charts, you will
see that the colors suitable for copper, gold and silver are labeled
Medium temperature/Medium expansion enamels, so you know they will
all work within this temperature range.
There is a relationship between the temperature of the kiln (within
these ranges for non-experimental enameling), and how long you fire
the piece. Many people choose to “high fire” which means using a
higher kiln temperature and shorter time for the piece to be in the
kiln. You can use a slightly lower temperature and fire a little
longer. For example, if you fire at 1500 degrees F, you might want to
leave a small piece of jewelry in the kiln for 1 minute, which at
1375 degrees F, you might want to fire for 2 minutes.
This is also not a mystery. Fusing enamel in a kiln is causing
predictable scientific reactions that vary with the specific
qualities of the enamel, the metal, and the heat. Enamel goes through
several noticeable stages while it is in the kiln. First, it looks
like powder. As it heats, it begins to fuse a little, and looks more
like sugar crystals. Then, in an early stage of fusing, it has melted
into one surface which has the rough texture of orange peel. Finally,
it fuses fully into a smooth glassy shiny surface. You can observe
these stages. How much heat and how much time are the variables that
you are working with.
If you think you have minerals in your water, use distilled water to
be sure that you aren’t adding any unwanted elements to the mix. If
you have a de-humidifier, the water that comes out of it is
distilled. Saves a lot of money to pour it into a water jug rather
than down the sink.
I have never heard that the quality of the air or the altitude
affects kiln enameling. What is really going on is the chemical
reaction from putting enamel under high temperatures.
There is a difference in oxidation on metals that surround the place
you want to enamel, and oxidation in the enameling process itself. If
you enamel a copper piece of jewelry, the parts of the piece that do
not have enamel on them will get oxidized, and that is called
firescale. These need to be removed, unless you want to use them as
an element of your piece. Fine silver doesn’t have this problem, but
it is softer. Sterling silver will oxidize. It doesn’t matter if you
heat - anneal - the metal before you put it in the kiln since the
kiln will anneal it anyway when it is fired at full temperature.
Many enamelists “set” their enamels into pieces of jewelry just as
jewelers’ set stones into a ring or brooch. This eliminates oxidized
metal in the setting, and allows you to use stronger/different metal
than fine silver.
If your enamel is chipping off, that is a problem of too thin metal
for the thickness of the enamel layers. Unless you are using very
thick metal, you generally counter-enamel the piece which means
putting a layer of enamel on the back of the piece so that the back
and front of the enameled piece have equivalent pressure pulling on
the metal. Champleve is a technique that allows you to enamel into
troughs or depressions in the metal without counter-enameling.
When you experiment with different colors of enamel, you will learn
which ones are more sensitive to heat. There is a difference from
color to color because they contain different oxides. Generally, reds
and pinks, for example, are more apt to “burn out” and turn ugly
colors if you heat them too high and/or too long.
Enameling is not magic; it is however, a complex art form in which
the scientific/chemical components of the materials as you heat them
play a significant part in your result. Unlike some other art forms
where the materials themselves are stable and non-players in the
eventual result, the chemical changes in enamel must be mastered to
create the results you want.
This isn’t just a pain in the neck; it actually gives you a huge
range of techniques available for your designs. And, you don’t have
to learn them all at once. To start, try the more stable transparent
blues and greens, and after you’ve enameled one layer, apply them a
second time slightly differently. You’ll get some beautiful results.
Linda Darty has laid this all out, step-by-step in her book The Art
of Enameling, and I’d recommend that as the place to start. Ruth Ball
is great also, and there are many other useful books.
Hope this helps,
Marcie
Marcia Rae Design
(VP- The Enamelist Society)