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Enamel flaking off copper after firing


#1

I’ve recently completed a batch (30) of enamel charms for a charm
swap I’ve entered but I had quite a bit of trouble with enamel
flaking off of the copper on several pieces. I used 18 Gauge copper
for the metal and throroughly sanded and cleaned each piece before
torch-firing. I also tried pickling and sanding after firing the
counter enamel on the back sides. Still, some chipping did occur and
in some cases the entire enamel surface simply popped off. I tried
using copper cleaner after sanding and then rinsing in clean water
and drying before firing but still some of the pieces just would not
allow the enamel to adhere, or some of it chipped off from the edges
while cooling. Very frustrating as I’m doing a 3 color overlay and
each firing results in more repair work. What can be causing this?
The environment is almost sterile!

TIA,
Chuck


#2

Enamel flaking. I don’t know what causes this problem, unless
something is contaminated. My advice is to ask: website Grains of
Glass… or on the Enamelist Society fb page. or, if Judy Stone is
lurking, maybe she’d offer a solution. Anyone reading this have an
answer?


#3

Hi Chuck,

Sorry to hear you’re having so much trouble with your enameling.
Unclean copper is the usual culprit but sounds like that is not the
issue here, so here are a number of other possibilities…

  • The most likely cause is too thick of a coating of enamel at a
    time. Enamel must be built up in thin layers.

  • Firing at the wrong temperature, or not long enough for the enamel
    to fully adhere. This is especially important for the first layer.

-Failure to allow the enamel layer to dry thoroughly before firing,
when using liquid enamel or liquid adhesive.

-Using enamel incompatible with copper. Make sure you’re using
enamel designed for copper, not steel or glass.

-The enamel is too old or contaminated.

Hope this helps. Good luck.


#4

Maria,

What happens to enamels when they get old. How can you tell when an
enamel is too old, before the firing and the flaking off that was
described?

Linda K-M


#5

what shape is item


#6

Or, the copper itself may be the problem. I spoke with Judy Stone
and that was her comment. I do remember waaay back in the dark ages,
when I made copper pendants hung on a leather thong, that I was
having horrible problems and it was related to some contaminated
copper. Cleaning couldn’t affect the problem. Had to replace the
copper.

Marianne Hunter


#7
  1. Is your copper piece domed? Less warpage and less stress that
    way.

  2. Using very thin layers of enamel, not very thick ones?

  3. Using counter-enamel?

  4. What brand of enamel? What part #?

  5. What temperature?

  6. Pinging off the front, the back, or both?

  7. How are you cooling down the pieces when they come out of the
    kiln? Is there a cold draft where the pieces are sitting?


#8

There are several possible causes for enamel flaking off the copper.
However, the main cause might be with the copper itself. For
enameling, it is recommended that one use oxygen free electrolytic
pure copper such as sold by Thompson enamel. Many do use plain
roofing copper with no problems, but I prefer not to take any
chances as In addition to enameled jewelry items, I do large scale
wall enamels, and the last thing I would want to happen is to have
some of the enamel flake off, possibly weeks after the item was
made.

Many years ago, Woodrow Wilson addressed this matter in one of the
articles appearing in Glass on Metal. He pointed out that when using
plain roofing copper, there was a possibility of enamel flaking off
months after a work was finished.

You mentioned doing a thorough cleaning of the copper, using a
copper cleaner. After using any copper cleaner, it is advisable to
neutralize thepiece thoroughly, before enameling.

Alma


#9

Are you torch firing? If so, you may not be getting the first firing
hot enough to adhere the enamel to the metal. The entire fired enamel
will pop off. Are you sifting the enamel and using several thin
layers? Too thick layers can cause chipping. Are you using opaque or
transparent enamel? If opaque, you only have to wipe the oxides off
with a paper towel before firing the front of the piece. Are you
cleaning the edges? what are you using to clean the edge?


#10

Billie,

I am torch firing using a hend-held MAP gas torch. I had one case
where the entire fired enamel counter popped off. I am sifting the
enamel using an 80 sifter. I may be putting it on too thick in those
cases where it chipped. For cleaning before firing and between
counter enamel and top coat I’ve done: Pickle with water rinse, 320
grit sandpaper, copper cleaner with water rinse and I’ve used all
combinations of the 3 cleaning methods but still have some issues.
I’m thinking, as has already been said, that maybe the copper itself
is at fault.

Thank you for taking the time to respond and thanks to all the
others who have responded to this thread,

Chuck


#11

I haven’t encountered this problem, but when I clean copper, I do
this:

  1. Clean it using Penny-Brite or sandpaper, rinse.

  2. Use an alundum stone under running water, for texture if I want,
    or for the edges between coats.

  3. Maybe brighten it using a fiberglass brush. Then rinse, making
    sure the water sheets off the surface and doesn’t bead up.

I don’t pickle it at all. It didn’t seem to serve any purpose and it
can attack some enamels. Also, I looked in a textbook I used as a
student, by Glenice Lesley Matthews, and she gave some more reasons
for cracking:

  1. Applying a thick layer of enamel on a thin piece of metal

  2. Enamel that has been cooled too rapidly

  3. Enamel that was damp when fired

  4. Enamel that has been fired for too long or at too low a
    temperature. Firescale can form underneath and then when the piece is
    cooled, the enamel can flake off because it never really attached to
    the metal.

I use a kiln, but I did try torch firing once, because I admire the
effect so much. There was the most awful cracking and discoloration,
and I had to put it back into the kiln to “heal”. So hope this
helps-- Susan