"Peter W.. Rowe," wrote in message
...
On Tue, 17 Apr 2007 22:59:52 -0700, in rec.crafts.jewelry Carl

wrote:

When C0nnie put fingers to keys it was 3/17/07 1:56 AM...

I want to do granulation in Argentium and fine silver. I'll keep y'all
posted...

What little I know of granulation says you need to be using an alloy and
that trying to do it with fine silver will be a problem. Do I need to
know more about granulation?

- C

yes, you need to know a bit more. Fine silver, or fine gold, are the
easiest to
granulate. Alloys are increasingly difficult as their melting points
drop.

Granulation is done by causing the surface skin of the granules to melt
before
the granule itself, or the base plate, does. This is done in several
ways. One
is to copper plate the granules. The usual method is to put the grains in
an
iron cup/container, along with some well used (turned blue in color)
pickle, or
just plain copper sulphate solution (about the same thing, used pickle
that's
already at hand is of course cheaper) The resulting electrolytic action
copper
plates the grains, which can then be placed on the desired surface,
usually with
a mix of dilute orgainic glue, perhaps a trace of flux, and water. .
Another
method is to glue unplated grains in place on the backing surface with a
mix of
organic glue (hide glue, for example) often a trace of flux, and a mix of
powdered copper salts. When this is heated, to glue carbonizes, and
causes the
copper salts to reduce to metallic copper, leaving traces of copper metal
on the
grains and in the contact areas. With the plated grain method, the copper
is
already there, so no reducing action is needed. Either way, then upon
further
heating, when the eutectic temperature between copper and gold or silver
(whichever is being worked) is reached, the copper then forms a eutectic
alloys
as a liquid on the surfaces of the grains, essentially becoming a faint
thin
liquid layer of solder on the surface. It's so little that upon continued
heating, the copper quickly diffuses further into both the grains and the
substrate, leaving the grains now affixed in place.


The powdered mineral Malachite ( Chrysocolla, Copper Carbonate ), has been
used for centuries as the Copper bearing salt in granulation work and other
fusion joinings of precious metals. The name Chrysocolla translates from the
Greek to "Gold Glue". Reference to the use of the mineral as a soldering aid
is found in the writings of Theophrastus ( 370 - 287 B.C.E ). In those days
they didn't use hide glue, they used Camel dung and juices from "almost"
dried fruits ( high fructose content ) to make the granules adhere to the
intended surface and act as the supplier of additional reducing atmosphere.

--

Don Thompson

Stolen from Dan: "Just thinking, besides, I watched 2 dogs mating once,
and that makes me an expert. "

There is nothing more frightening than active ignorance.
~Goethe

It is a worthy thing to fight for one's freedom;
it is another sight finer to fight for another man's.
~Mark Twain

~~~~~~~~~~~~~~~~~~~~~
A further method, better suited to lower karats (not too low, but say,
18K) can
be done by first heating the grains repeatedly in an oxidizing atmosphere.
This
causes copper oxides to form on the surface, and copper near the surface
of the
grains to diffuse towards the surface and concentrate there as the oxide.
The
layer of metal just under the surface ends up copper depleted slightly.
In any
case, you've got a higher percentage of copper at the surface, as oxide,
than in
the alloy itself. These grains are then glued in place same as for other
methods, and heating lets for formed carbon (from the glue) reduce the
copper
skin surface to copper, and from there the process is identical.

High karat alloys, or pure metals, are easier to granulate simply because
the
difference between the temperature where bonding takes place, and that
where the
substrate or granules actually melt on their own, is greater, allowing
easier
working without melting accidents.

As to the original question, whether or not argentum silver granulates
would
depend on whether a copper layer on it's surface lowers the metling point
at the
interface between the two, and on whether the resulting eutectic bond
formed if
they grains can be affixed this way, is strong enough. Some alloys can be
granulated, but the results are not satisfactory since the joints are so
brittle
the grains fall off again too easily. I don't know if this is the case
with
argentum, but I'd not expect it to be.

fine silver, though, is relatively easy to granulate.

Peter Rowe