I am doing some work with my students with PMC3. I have never use it
before. I’ve always used PMC or PMC+ and fired it to 1650. The PMC3,
fired strictly according to directions at 1290 F, seems to remain
ridiculously brittle and nowhere near strong enough. This seems odd
to me, as the directions claim that PMC3 is the strongest, densest
PMC when fired as directed.
I guess I can fire the PMC3 to 1650, but its claim to fame is
supposed to be that you don’t have to. Is higher firing the only way
to get strong enough metal to make rings that are reasonable
thickness? And that can be stretched a little if necessary?
I would really appreciate help on this, as I am frustrated with my
students’ pieces breaking so easily. The results are really not
acceptable. And they want to torch fire!
Hi Noel… my first experience with this was the same!
Yes fire it long and high (just as the lower versions - 1650 for
designated time) and you’ll be good. My lower fired versions were
breakable with my fingers, but once I fired them like the earlier
pmc versions all was well (making me wonder why I needed - or why
they produced the PMC3).
I only torch fire pMC3 and have found that if I torch it as
instructed, quench and then I torch it again it comes out firly
strong. I’ve even hammered it at that point. Burnishing, especially
tumbling with steel shot then seems to vastly improve its ductility.
I don’t know how the torch temp relates to kiln temp though.
When firing silver metal clay, there are many firing options
available. The absolute “strongest” you can reach will be achieved by
firing the PMC3 at 1650F. This will increase the shrinkage. I do not
believe that anyone claims that the 1290F/10 minute schedule will
result in the strongest/densest result, if someone makes this claim,
they are misinformed or have misinterpreted the technical data.
Unfortunately, the published technical data often inadvertently
leaves out some detail that allows people to make such
misinterpretations and you really have to read all the charts to
achieve a full understanding. For technical on the
tradeoffs on the firing times and temperatures, please see the
following at the PMC Guild website:
While this compares the two brands of low fire silver clay, it
contains the most published data on strength, density, and shrinkage
available. Alas, it does not contain the full results of the testing,
just selected results and interpretations.
I too have had disappointing, brittle results with PMC3 fired at low
temperatures. But fired at 1650 for 20 minutes my PMC3 rings are
strong. Still, I prefer to fire them for one to two hours for even
more strength. There are charts on the PMC guild site about this.
I don’t stretch my PMC rings, but it would be interesting to do some
tests. I prefer, if necessary to finesse sizing, to add or remove
material from the inside of the ring. Tumbling will work harden rings
but obviously wouldn’t solve the brittleness issue.
Since your students want to torch fire, I think your problem is
solved. With the torch you can hold the temperature very high and
get maximum shrinkage in ten minutes or less. You can see the
shrinkage happening. I do some pieces this way and find the resulting
silver to be very dense and not brittle.
Part of the appeal of low-temperature firing is firing stones in
place. One solution for strong rings is to fire the shank at high
temperature, and separately fire the stone setting at a lower
temperature, then use paste, slip or oil clay to join them and fire
once more at the lower temperature for a long time.
I am doing some work with my students with PMC3. I have never use
it before. I've always used PMC or PMC+ and fired it to 1650. The
PMC3, fired strictly according to directions at 1290 F, seems to
remain ridiculously brittle and nowhere near strong enough. This
seems odd to me, as the directions claim that PMC3 is the
strongest, densest PMC when fired as directed.
Noel - Rings are notorious for taking abuse. I would fire to 1650 for
any ring if at all possible. (Actually, I would fire to the maximum
for anything I could - I think it makes the silver stronger.) I most
certainly would not recommend torch firing any rings - keeping the
temperature at the needed constant for the entire ring for the length
of time required to torch fire properly is almost impossible for most
people to do. I would consider stove firing if such an option was
available because the flame is more constant. I wish I had a better
answer for you.
The short answer to your question is indeed longer firing times at
higher temperatures will result in much stronger pieces. PMC3 is the
strongest of the 3 versions, but only when full sintering takes
place at the highest temperatures.
I will only make rings of PMC that are thicker and heavier. Dainty
little rings won’t hold up to the wear and tear of regular use. I
may be alone with this opinion, but I don’t necessarily think fine
silver rings, in general, are the most practical because the high
abuse rings get and the softness of the metal.
I think a longer answer to your question may be more satisfying, but
a bit of history about Metal Clay may be needed, bringing light and
understanding to the brittle MC issue.
When Metal Clay (MC) was first marketed, it was marketed to the
hobbyist. Reason being is in Japan, where it was developed, they
have a majority of hobbyist and manufacturers. Unlike in the US,
where there is a much larger middle level of professional artisans.
Because MC does not make sense for mass manufacturing, they selected
the hobbyist for their target. Their aim at that time was to make a
product that had quick results – that meant low firing times. In
general, the philosophy was to provide a product that had “Perdy”
results quick and easy. Unfortunately, at the time longevity of the
product was not a focus.
As the products popularity grew and developed the pioneers and
artisan users of MC realized that the “professional artisan” out
there using this product in the US wanted more from it. They
demanded, not only beauty, but also stronger lasting results, and
new methods that would get them there. Among educated regular users,
longer firing times were explored as well as modified constructing
techniques that are best for MC vs regular silver smith work. They
realized all though you “could” fire at lower times, that didn’t
mean you “should.” So the general rule of thumb is to fire as high
as you can and as long as you can for the project with consideration
of gem and other inclusions.
My gripe with the manufacturers is that they still have not made
these basic concepts clear to the consumer. They still provide
firing schedules that put an emphasis on the lower firing schedule
verses the importance of the longer firing. Luckily, there are lots
of books and teachers, and websites that do discuss these concepts,
but I wish the manufacturers would catch up.
Education and experience is certainly the key to the success for
both you and your students.
I am doing some work with my students with PMC3. I have never use
it before. I've always used PMC or PMC+ and fired it to 1650. The
PMC3, fired strictly according to directions at 1290 F, seems to
remain ridiculously brittle and nowhere near strong enough.
whilst I’m rather new to PMC in general myself, I’ve been taught
that to make the metal stronger ramp time and cooling methods are
important. When firing PMC3 I do a 2 hour ramp to target temperature
of 1290F, hold for 10 minutes, then let the object cool inside the
kiln. I don’t open the kiln’s door, I just leave it in until it’s
cool which takes several hours. I never quench my pieces. With this
method I haven’t encountered problems yet, but like I mentioned, I’m
new to this and still testing.
Education and experience is certainly the key to the success for
both you and your students. I hope this helps.
Yes it does, thank you. I just feel like a sap for having faith in
the instructions. I always fired my PMC and PMC+ to 1650 for 2
hours, though I don’t really use them in my own work any more. So I
knew better, but for some reason I thought by now the instructions
would be honest and accurate. There is no mention in them that it is
even an option to fire higher, let alone a recommendation.
Please excuse me if I said these things here yesterday. I’m really
fuming. I let myself end up teaching in a situation I wasn’t totally
on top of, and I don’t like the feeling at ALL. And I find it
nothing short of shocking that the company’s literature is so
totally misleading. PMC3 has “increased strenth [for] rings,
buckles, bracelets” and “95% as strong as rolled fine silver”. Hah!
These things are right next to the firing schedule-- 1290 for at
least 10 minutes, 1200 for at least 20 minutes, or 1110 for at least
30 minutes. Nothing about 1650. I fired to 1290 for 30 or 40
minutes, and pieces snapped in my fingers.
When firing PMC3 I do a 2 hour ramp to target temperature of
1290F, hold for 10 minutes, then let the object cool inside the
kiln. I don't open the kiln's door, I just leave it in until it's
cool which takes several hours. I never quench my pieces. With
this method I haven't encountered problems yet, but like I
mentioned, I'm new to this and still testing.
This is interesting. I think I read that it was a good idea to ramp
up PMC asap, though I’m not sure I read that, or where. I’ve always
fired it as fast as I could, but of course temperature AND time are
factors, and you’re doing a VERY long firing.
This is interesting. I think I read that it was a good idea to ramp
up PMC asap, though I'm not sure I read that, or where.
For the PMC alone, ramp speed does not matter. If you’re using a
combustible core, such as Cork Clay, then you want a slow ramp speed.
If your clay was a little damp, you may wish to go with a slower ramp
speed.
At home, I use a slower ramp speed to prolong the life of my poor,
abused kiln. When teaching workshops I fire:
Ramp Speed 4 or 5 (with 5 being the top) 1470 for 30 minutes.
Another option for workshops is to fire at 1650 for 20 minutes.
It takes longer to reach temperature, but then doesn’t hold as long,
so it should come out about the same.
whilst I'm rather new to PMC in general myself, I've been taught
that to make the metal stronger ramp time and cooling methods are
important. When firing PMC3 I do a 2 hour ramp to target
temperature of 1290F, hold for 10 minutes, then let the object cool
inside the kiln.
Isabella, the ramping up and cooling down time you describe are only
necessary and yes important when you have a sensitive inclusion, such
as glass or a gemstone. What happens if you do either too quickly is
thermal shock, which can crack the inclusion. The real thing that
determines how strong a piece will be is the target temperature and
the length of time it is at that temperature.
There are two reasons that PMC3 or any metal clay would be truly
brittle or fragile after firing…it was not fired at the correct
temperature for the correct length of time OR it was made too thin.
The manufacturer’s supply the parameters for temps and times for
each of the different formulae, but (and there’s been some discussion
on the metal clay Yahoo forum about this) I recommend firing all
formulae at the highest temp (1650 degrees F) for two hours. You can
fire longer, but not at a higher temp (or the object will melt).
I always quench my metal clay objects. I’m just too impatient to
wait for them to cool. I doesn’t seem to effect the strength of the
objects.
Here’s the caveat: precious metals from metal clay are not rolled
metal sheet. They have not been compressed/work hardened by rolling
through a mill. They cannot be forged, bent, ‘adjusted’ the way
sheet metal can. There is some room for ‘movement’, but not nearly as
much as with rolled sheet.
Just a note: the lower temps and shorter firing times were developed
to allow stones, pottery, glass, etc, to be imbedded in the clay and
fired along with it. Since many metal clay users might have been
unfamiliar with traditional jewelry/metalsmith techniques, the
manufacturers devised the lower temp/shorter firing formulae to
assist them in ‘setting’ those objects. Additionally, these
formulae, specifically PMC3, produce a much stronger, denser object,
especially when fired at the higher temp/longer firing schedule.
There are two reasons that PMC3 or any metal clay would be truly
brittle or fragile after firing...it was not fired at the correct
temperature for the correct length of time OR it was made too
thin.
Additionally, these formulae, specifically PMC3, produce a much
stronger, denser object, especially when fired at the higher
temp/longer firing schedule.
Yes, these statements are true, almost. You should substitute the
word “only” for “especially” in the second. The problem is that the
“correct” firing schedule for producing a “stronger, denser object”
is an hour or two at 1650, and this recommendation is nowhere to be
found on the PMC3 packaging and literature. By the same token, pieces
fired for half an hour at 1290 (“at least 10 minutes” recommended)
are by no means dense or strong, pretty much regardless of thickness.
This is unacceptable and needs to be changed-- who could fail to
agree?
I had previously made some bead caps that cracked readily upon
forming when I had fired them accoring to the instructions for PMC3.
I was advised to fire them longer at a higher temp (1650) and hey
presto they reacted like real fine silver and were fine for forming!
So… the shorter lesser temp is a useless piece of if
you plan on doing a real work with it! Fire it just as the original
PMC and you should be fine!