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Enamelling Cracks Trouble


I just recently starting doing some enamelling again, I finally have
my own kiln (thanks for everyone’s help with that search, by the
way!). I created a few pieces in PMC & then put enamel on them, and
for the most part everything is going well, going as expected, but
this one piece really has me stumped. It seemed to be just fine, and
I was quite pleased with the results, and then suddenly a couple
days later I noticed some cracks in the enamel & I can’t seem to get
rid of them. At first, I thought it was because I was cleaning up the
edge with a burr & it slipped, so maybe I smacked it. I hadn’t
noticed the cracks before that, but they may have been there. I
figured I’d just re-fire it & the cracks would go away. I refired
it, and they came back, maybe even a little differently. I tried
adding another layer of enamel & firing it, but they were still
there. I tried another, but it seemed the top layer was OK & then the
cracks were still there below. I tried once more, firing it longer so
that hopefully it would all blend together, but the cracks just keep
getting worse. It’s a pretty thick piece of metal, about 1.6mm thick
(although with a stamped pattern impressed into it), and overall the
enamel isn’t thicker than that, so it seems hard to believe that the
enamel would be too thick. Especially since when they first
appeared, there was even less enamel on it (wet packed into the stamp
impressions, then just two layers dusted on top). Here is a link to
a photo of it when I first saw the cracks:

I could take another of how it is now, too, if that would help. They
are really obvious, worse than in the photo, you can feel them when
you run your finger over it. Maybe I need to file it down, try to
remove as much of it as possible & then start over. I’ve just never
had this happen, so I don’t know the best way to fix it. Or, for that
matter, why it happened & how to prevent it from happening again!


Designs by Lisa Gallagher

Hi, Lisa…could it be that the thick piece of PMC wasn’t fired
long enough. I have been firing everything, Standard, Plus, and 3 at
1650 degrees for 2 hours. There may have just been something about
the PMC that caused the cracks.

I have a different thing about PMC…(been using it for several
years and love it). Decided to melt the old pieces to cast in
Cuttlebone. Wow - what a mess. Even with the fully fired PMC there
was the worst thick stuff in the crucible, and I could hardly recover
any “liquid” silver for casting. Seems the binder is very dense!!!

Really am learning a lot from all the threads on Orchid - thanks

R M Christison


I looked at your pic and it appears the enamel cracks are located
above the area where the metal hanger transitions to the thinner part
of the pendant. That just screams to me of “different rate of
cooling” issues. The greater bulk of metal where the
pendant-plus-hanger retains the heat is in contrast to the thinner
metal of most of the pendant.

As you cool the enamelled pendant, the thin areas will go through
the glass transition temperature first, the enamel above the heavier
hanger will do their glass transition later. If you can move through
that temperature range much slower, I think you’ll reduce the
stresses in the enamel and likely eliminate the cracking. There’s
every hope you can re-work the pieces with better cool-down ramp

Are you removing the pieces too hot? Or are you venting your kiln to
speed the cooling? Those would be asking for trouble. Where you have
discontinuous metal thickness, you need very slow cooling through
the glass transition. We actually use time/temperature programmable
controllers to manage the heat-up ramp and cool-down ramp perfectly
repeatably. A thermocouple tells the controller what’s happening and
the controller ensures the slow cool-down gradient that we
programmed. We use inexpensive (about $260) Shinko PCD-300 series
controllers from Shinko of America, where the wonderfully named Jim
Miracle is very helpful. You can Google them easily.

Or while cooling, you can manually hover the kiln j-u-u-u-st above
the glass transition temp for a half hour and then cool it, fully
closed, as slow as you can, with absolutely no venting and NO OPENING



Did you counter enamel your piece?

jennifer friedman
Ventura, CA

As you know, glass has two temperature ranges where it’s vulnerable.
One is somewhere between 900-1200F where it “aneals” and the other
from there on down where it’s vulnerable to “thermal shock”. Which
temperature range are you referring to when you use the term “glass
transition” temperatures. The former can lead to glass cracking some
time after the glass has cooled (poorly anealed) while the latter
causes cracks during the cool down period.



I guess you’re ‘talking’ to me? Both those temperature ranges are
important. But it’s not easy to give out specific numbers because
the ID of the glasses that end up in enamels is the first problem,
then the additives make it even harder. Graphs of the thermal
expansion coefficient in these products are roller-coaster shaped.
Take a look at

not for a solution, but to note the problem in more detail.

The glass and additives in each enamel require our time-temperature
profiles for the controllers to be enamel-specific. It’s sufficient
of a black art that it gives me sympathy for those who end up using
epoxies! For the 2000 Sydney Olympics, most of the badges and pins
were cast or coined in China and hand-syringed with epoxy. A local
manufacturer here managed to get an order for some high-end pins and
badges, promising glass enamel on precious metals. He lost his shirt
with cracking issues.


Thanks, everyone, for your replies.

Jennifer- No, I didn’t counter enamel it. It’s meant to be a silver
piece with decorative enamel on it, so to put enamel on the back
would ruin that effect. I think, though, that the silver piece is
thick enough to not need it. It’s certainly thicker than other pieces
I’ve successfuly not counter enameled, plus the enamel isn’t as thick
as the metal.

Mark- > That’s certainly an interesting thought, I don’t recall that
ever being a concern when I took my enamelling classes, but either
that just never came up with what I did, or it’s been too long for me
to remember that (certainly a possibility!). I am pretty sure,
though, that in those classes there was never a cooling and
reheating of the kiln. One person would put in their pieces, fire
them for a few minutes, take them out to cool, and the next person
would put theirs in. To answer your question, then, I do just do the
firing & take it right out, just as I always have. This is my own
personal kiln now, though, and as for having the kiln adjust the
temp, I have a digital control on my kiln, so I can quite easily have
it do whatever I need. Don’t I risk overfiring, though, asking it to
fire for only a couple minutes & then cool down? It would seem to me
that the timing needs to be relatively so quick that it would be at
the firing temp, that it would still be very close to that temp for
too many more minutes as it tries to cool down.

RM- > (I’ve gotten that from someone else, too) I suppose that’s a
possibility. I did, though, fire that one at the same time as
another, even thicker, piece, and the enamelling on that one worked
like a charm. That brings up the issue, though, of how do I really
know it’s fully fired? I mean, it “clinks” like it’s solid metal, it
shines up like metal, it looks fired. I had some earrings I did,
though, actually my first piece in this kiln, that when I put them in
pickle later (I added ear wires & soldered them closed), everything
turned a muddy brown, including other things I had in the pickle at
the same time. I reheated them with the torch & they cleaned up
fine, then- in fresh pickle. I’m not sure if maybe I didn’t fire the
PMC long enough, maybe it wasn’t fully fired. I’ve been told many
times that every kiln is different, just like regular ovens. So if
one person, for instance, fuses glass at 1500 degrees, mine may fuse
at a different temp. Actually, it seems mine fires at a VERY
different temp, though, like 1640. Does that seem a little TOO
different to anyone else? I’m still tweaking that calculation, but I
don’t imagine I’ll get it much lower. And then what does that mean
for the firing schedules packaged with the PMC? I mean, with the
glass it’s easy to see if it’s actually done. Enamel, too. It’s
fused or it’s not. With PMC, I’m not so sure how to tell. If my kiln
fused glass 1050 degrees hotter than what I’ve heard is “the fusing
temp”, does that mean everything else should be that much higher in
my kiln, or at least a fair amount higher? I seem to be able to
enamel successfully at 1575 for 1.5 to 3 mins, which is about what it
seems it should be. I fired my first PMC+ piece (the earrings) at (I
think) 1650 for 10 mins (maybe a little higher & a little longer).
Maybe since my kiln seems to need to read hotter, that wasn’t hot
enough for that length time. Since I feared maybe it hadn’t fired
well enough, I did the next batch - this cracked piece & one other
piece - at 1600 for 20 minutes. That’s then basically the lowest
temp at the middle time. Maybe I need to try doing it for longer at a
higher temp, just to be sure, but as I mentioned before the other
piece seems to be fine. I liked the idea of only firing it for 30
mins or less, but I suppose I need to be more patient to make sure
it’s done right. Anyway, though, once again, how do I know it’s done?
Oh, and thanks for the mention about trying to melt the PMC later,
I’ll certainly keep that in mind!

Sandi- You asked, too, if I counter enamelled, but also suggested
that maybe the COE might be different. Now, if I bought them both
from the same series through Thompson, shouldn’t they be the same?
When you ask about getting all of the chemicals, etc, out of the
enamel, do you mean it being fully fired? I’m not sure what other
chemicals there might be. I didn’t do any soldering or pickling or
anything before (or during or after) I enamelled it. I also burnished
it as much as I could (lots of little crevices) before enamelling, to
try to “close the pores” as much as possible, as I’ve heard it’s a
bit porous after firing. I guess, as you suggest, the best thing to
do to try to get it back to where it needs to be is to start over
with the enamel. Thanks for the suggestion on how to get a fair
amount of the enamel off. Maybe, though, I can just try to get the
top coat off, not all the bits down in the design area? I think if I
have to get every last bit of it off, I won’t be able to do that
without risking the design, in which case I would TOTALLY start over
& figure out what to do with this piece of enamelled metal (sniff).

Designs by Lisa Gallagher

OK, if you purchased your enamels from Thompson, and got them from
the same basic grouping, their COE will be the same. So that’s
probably not the problem. As for getting the chemicals out - if you
are sifting on your enamels, you want to sift them down to 80 mesh
before putting them onto your piece. If you are wet-packing, you
want to wash your enamels until they are clean before putting them
in. I fire at 1420-1450 for approx 2 minutes, but every piece varies
and kilns also vary. It sounds as if yours is way off. You may need
to check the true temp that your kiln is firing at. The easiest way
to do that is to check it with pottery cones. I think that Tonya at
Whole Lotta Whimsy may have a testing kit available for this
purpose. If you are firing that far off the temp setting on your
controller, contact your kiln manufacturer and get a replacement
thermocouple and replace it. Something is just not right there. As
for your Metal Clay - I routinely will fire my pieces at 1650 for 2
hours whenever possible. It guarantees that I have the strongest
sintering I can get. Even though I can fast-fire at 1650 for 10
minutes or 20 minutes, I prefer to maximize the time unless I have
inclusions such as CZ’s, stones, or glass that would call for other
temps or time frames. And, no matter the thickness, I would always
counter-enamel. The stresses almost always need that extra step. Good
luck with the re-do of the project.

Sandi Graves, Beadin’ Up A Storm
Stormcloud Trading Co (Beadstorm)
Saint Paul, Minnesota USA

an alternative to washing your enamels is grade sifting down to 200
mesh. if it’s good enough for david freda…
it’s good enough for me.

good luck
smile…be happy

Regarding enamel cracking…

Sorry I’m coming in late to this conversation. But! I’ve had the
same troubles, and near as I can tell, it’s always been due to either

  1. No counter enamel…I’ve actually gone back and counterenameled a
    piece after the cracking, and had the cracking go away, so this can
    definitely be a cause. It doesn’t matter if the metal is thicker
    than the enamel, in my experience… I think it’s the differential
    cooling time (between metal vs glass) that causes it…

  2. Too much air movement in the kiln area just as you bring the
    piece out. I solder in the area where my kiln resides, and if I
    forget, and leave the fan on “high”, I get cracking.

Ack. Also, sometimes in the summer I have the fans blasting
everywhere, and can get the same deal.

Barbara Louise Bowling
Louise’s Leap Studios
2700 Harmony Street