Does anyone have any suggestions as to why on the third firing
in kiln a pendant would melt. I was making a 2 1/2 x 2 1/2
domed pendant from 20 ga sterling silver with fine cloissone
wires and counter enameled each time. On the third and what I
thought would be the last firing the piece collapsed at the
points where it was held on a trivet. The fine wires did not
melt. It appeared that only the sterling silver base collapsed.
Could it be that the piece was too heavy to be fired on a trivet
in that the weight was not evenly distributed. Someone suggested
firing something like this on a piece of mica to distribute the
weight evenly during firing. Should I not have used sterling as a
base but fine silver instead. The pyrometer on the kiln did not
go over 1500 with each firing. Thanx Miki
Hi Miki,
You should be fine with 20ga sterling sheet in your enamels,
although I would suggest switching to fine silver, it is not that
much more expensive and it behaves perfectly in the kiln. I am
not sure what you mean when you say that the edges of your piece
collapsed at the trivet contact points; if the metal actually
melted, I would say it is time to calibrate the kiln. However if
the piece just kind of slumped I can offer two suggestions: first
get more support on the edges of the piece, I have had larger
circular peices warp at the unsupported edges, second how long
are you firing for? 1500oF is a pretty hot kiln, I never go
longer than 2 min at that temp, less if I can get away with it,
you may want to check the specs on the enamels you are using and
go with a temp right at the flow point for the highest temp
enamel in your piece, then keep close track of how long it takes
for the enamel to flow and don’t exceed that time in each firing.
I strongly suggest investing in a good digital timer with a nice
obnoxious ringer on it.
Hope that helps some!
Nikki
Hi Miki – One thing to consider is the amount of counter enamel
you are using. Once you have a good coat, with no holes in it,
you don’t need to add more – especially since you will
eventually be stoning down the front side of the enamel. I’d
also think about whether your kiln is holding it’s temp correctly
– you may be getting a hotter kiln than you think. Laura
lwiesler@att.net
Hi, I was just thinking, strange as it may seem. In dentistry we
use a mineral fiber to support our frameworks with the unfired
porcelain on them. It comes in pads that can be cut to size.
It is totally inert, and can take temps past 2000 deg F. If
anyone is interested, e-mail me and I’ll get the info on where
to get it.
Regards,
Skip
Skip Meister
@Skip_Meister
N.R.A. Endowment &
Certified Instructor
in all disciplines
Certified Illinois D.N.R.
Hunter Ed, Instructor
Nikki, I would also recommend a check of your pyrometer - 50
degrees higher temperature than your pyrometer reads can cause
collapse in sterling. You can get a box of temperature pellets
from Rio Grande or other suppliers in the casting/burnout oven
section to recalibrate your pyrometer. They come in 1300 and
1500 degree pellets, perfect for enameling callibration. Another
suggestion is to use fine silver since the melting temp is
higher, it gives you a wider margin for error.
Donna in WY
Looks like a consensus has been reached on the fact that the
piece was fired at too hot a temperature and that you should
probably find an accurate pyrometer for your kiln. Keep in mind
that sterling silver has a lower melting point than fine silver
and that you have to fire it at lower temperatures than fine
silver. The same thing goes for fine silver cloisonne wire on a
copper piece. Copper + silver= blob if you’re not careful and
I’ve seen many pieces where silver cloisonne wire has sunk and
disappeared into copper when fired at 1500 F. Stick to fine
silver cloisonne on a fine silver base, get a new pyrometer and
hopefully your problems will be solved.
Juliet Gamarci
@julietg1
HI Miki:
I just returned from a trip and have been scanning the 345
E-Mails. I think you may have some process problems. How long
are your firings? Also your temperature seems
excessively high. I have enameled on Copper with fine silver
wires which will disapear at 1475 F. so have been using 1450 F.
for ALL enameling eversince, for over 35 years. Going any higher
is just not really necessary. Firing is a matter of both time
and temperature and conservative here is the best in the long
run. Try a bit longer at a lower temperature and you will gain
much in control. Think you may have over heated the 20 ga.
sterling. Fine Silver will hold up better, also I suggest using
only 18 ga. for cloisonne’. I realise that doming should take
care of the tension between the upper enamel and the counter. But
maybe it was just a tad large in size for the thickness of the
sterling in porportion. I realize that 18 ga. will add more
weight, but will also add eons to the wearability and longevity
of your work. After all you are putting in major time, which
should reflect your integrity as an artist to produce a work that
will hold up for 1000 years or more! I have seen cloisonne’
pieces in museums that look like new even though they are 800
years old or more!
As for using mica, it just won’t work to back a domed piece.
Mica doesn’t bend, especially a compound curve. You also then
would not be able to counter enamel as it would be sticking to
the mica. Ugh! A mess. Speaking of counter enamel, what did you
mean when you said you counter enameled each time? Try just
applying the flux to the front surface after preparation of the
sterling, fire, apply counter enamel to back, fire, apply wires,
fire, add enamels to cloisons, fire and complete piece. I only
apply counter once. But I apply the counter almost as thick as
I think the finished top layer will be. It is not necessary on
a domed piece to have the counter enamel exactly the same
thickness as the top side since the curved surface of the dome
should alleviate any stress between
the metal and enamel.
I usually fire around 3 minutes depending upon the type of
enamel I am using. Best to look, or take a peek, after 2.5
minutes. Some enamels may take much longer to mature. Just ask
more questions as it’s the only way to learn and good firing,
Pat