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[Enamel Bits] Enamelling on brass


#1

I have just seen an antiques programme on the television, they showed
an enamelled urn. The expert said it was brass. I have also seen
Chinese cloisonn� enamelled beads, brass base and wires. I have always
understood that brass was a “greasy” metal and would not enamel, (in
fact I have tried it and failed ).

Has anyone a theory how the Chinese did it, could the brass be plated
before they enamelled? The urn was gilded and the beads were silver
plated, but I thought this was done after all the heat work was
complete. Ann Simcox


#2

Thompson Enamel supplier has a wonderful (about $6.) blue booklet on
enameling info. You can enamel on brass, but I think you let it
oxidize, and the enamel sticks to the crude on the brass, all the
oxidation. In their wonderful book it tells about enameling on all metals including aluminum!
Good luck don’t give up-


#3

Hi Ann,

     Has anyone a theory how the Chinese did it, could the brass be
plated before they enamelled? The urn was gilded and the beads were
silver plated, but I thought this was done after all the heat  work
was complete. 

You can enamel brass. I believe that Thompson Enamels still supplies
enamels to do so. They have been formulated to fuse at a relatively
low temperature and have, I believe, a higher expansion coefficient.

I have used traditional, non leaded enamels on gilding metal (Cu:Zn
95:05) and jeweller’s bronze (Cu:Zn 80:20). It is tricky and the
results are “unpredictable”, especially with transparent enamels.

Note that the Chinese cloisonn� enamels are invariably opaque with a
limited number of hues, probably because these were the ones that
worked.

In medieval Europe, copper champlev� enamels were gilded by
dissolving gold in mercury which was then used to coat the copper. The
plaques was then warmed to evaporate the mercury. So where did the
mercury go? And isn’t a silver filing in one’s tooth done in the same
fashion? Is metallic mercury in vapour form as toxic as ionic mercury
or methylated mercury?

L


#4
   ...The plaques was then warmed to evaporate the mercury. So where
did the mercury go? 

It is evaporated. Upon hitting cooler air, it most likely
precipitates again, I’d guess as very finely divided particles, that
then settle out. If you heat the mercury mixed metal in a closed
container and feed the fumes to a condenser, you can condense it back
out and reclaim it. In medieval times, if they did this, it was
probably not real efficient. So a fair amount of the mercury fume can
be presumed to have ended up in the workmens lungs. Where it most
certainly is toxic.

   And isn't a silver filing in one's tooth done in the same
fashion? 

Not quite. The mercury filling is never heated, What you end up
with is a silver amalgam, which for all intents and purposes, can be
thought of as an alloy of silver and mercury, with the main difference
being that it does not have the regular ordered crystaline structure
of an ordinary alloy that’s been melted and allowed to solidify.
Everyone worries about whether silver in fillings is toxic, but so
far, all research has suggested that the mercury in that amalgam form
seems stable and is not causing toxicity problems. Still, many
prudent dentists and patients are not taking chances with silver
filling anymore, just in case.

Is metallic mercury in vapour form as toxic as ionic mercury or
methylated mercury? 

Toxic, yes. But nowhere NEAR as toxic as some of the other forms,
such as methyl mercury as you mention. Thats the compount that a few
years ago, made the news when on brief, minor exposure to a lab tech’s
hand, covered with a latex glove, still absorbed enough through the
glove (which turns out to enhance absorbtion) and skin, from just that
one drip, to kill the poor lady. Took many months, but still killed
her. A HIGHLY potent neurotoxin, as I recall. Metallic mercury, if I
recall right, tends to accumulate in fat deposits, where it’s not
eliminated. It too causes neurotoxic effects, but so far as I know,
it takes a lot more of it, and more time.

Peter Rowe


#5

Near San Jose, California there is a place called Almadden. The
original Almadden was the source of mercury in Spain. But various
locations in the west yielding mercury were called by this name also.
Anyway, this mercury mine was very important during the gold rush days
when it was used to extract gold. The concentration plant was on the
premises too. Big metal flasks held the refined mercury. The posted
visitors pointed out the high death rate and low birth
rate recorded in the town.
Rose Alene McArthur @O_B_McArthurs