I apologize as this is really somewhat off topic. First some of you
on this list may wish to visit http://www.apecs.com.au/technical.htm
- this site as two articles of great interest to many, one in
particular that will be of interest to many, Alloying in the Small
Shop, its worth the look.
Although this dose not answer the question directly as this (below)
is instructions for alloying, it is the best I have seen. (The ingot
made is for putting through a rolling mill, target, i.e.
investment/mold, would apply more often.) What is said here applies
except for the adding of copper or other metal, but casting is easier
than alloying. Disregard the “not following directions” as often some
of what is in print is rather unclear (they assume you already know
something) and this may be the problem, the incomplete knowledge of
procedure.
Moreover it may be helpful to list what torch you are using from a
troubleshooting standpoint, the tip used may not be the right size
and needs to go up in size/type. Someone on the list no doubt uses
whatever type you have and may be able to give an answer, for example
if using converted acetylene equipment (different tips allowing it to
burn propane), typically this burns at 1850F. Not much of a margin
when the cubicle and amount to be melted are taken into account, a
can of mapp will boost this (it still is cleaner than acetylene).
Then again Smith puts out a real honker (tip) for propane, 76,000
Btu. That is why it may be useful to know what torch is used, as
someone on the list most likely uses that for some casting and could
say “this is what I do,” tip used etc., simply copy the move.
It is often some small thing over looked that causes the most
problems, preheating the crucible before adding the silver to melt
may make a lot or all of the difference, a cold crucible may be the
problem, the heat on the silver being transferred to the crucible and
“lost.” Sometimes as with an oxy/acetylene torch preheating the
crucible, using the largest tip and Toning Down the flame (a reducing
flame) can make a difference in success. As a note with air/acetylene
used for construction a larger (or largest) tip with the flame toned
down is (depending on size of work) best when soldering the bezel to
the plate. It makes life easier and more pleasant rather than
cranking up a smaller tip, think soft and broad.
Below is an answer to some of this, far different than what I asked
(English is their second language), but as said this is the best
directions I have seen, and was pleased to read it. Martin and D=F6rte
Planert are gold smiths, Australia. Regardless of torch, as they are
referring to the one I have, this is proper procedure for alloying
(and in general applies to casting). Note that if using an investment
to cast a ring or such it should still be hot and used right after
the wax is burned out. It will stay warm enough to allow you to do
the preheating of the crucible (such as used on a centrifugal caster)
to insure a nice cast.
"We have successfully cast silver and gold alloys for normal
workshop applications. As for gold we are usually alloying around 30g
18ct Yellow Gold at a time, never experiencing any problems. Alloying
Sterling Silver requires a large amount of heat over a longer period.
Always preheat the ingot to let the moisture evaporate to a bit more
than hand warm, then preheat the crucible until the inside is
glowing. Remember to melt the fine silver first and then fill in
slowly the borax coated fine copper (preferably small and thin
pieces). Keep the crucible moving to ensure the formation of a
homogeneous alloy. In addition use a graphite stirring-rod to stir
the molten metal, to assist in mixing. This also helps to detect
solid copper parts. If necessary add a little more borax powder and
keep heating until the metal displays a mirror like surface and moves
around freely in the crucible. Make sure to keep the distance between
flame and metal the same while moving the crucible towards the ingot
for casting.
Unsuccessful melting of metal is usually caused by:
An incorrect distance between flame and metal,
flame too small,
crucible not preheated,
copper added too early,
no flux used or
draught cooling the surface.
There will always be someone unable to follow instructions and then
complaining about the product, not detecting the actual cause: lack
of skill.
Regards
Martin & D=F6rte Planert"
I hope the small bit of may prove useful to someone, not
so long ago I needed all the help I could get. Again, please take a
look at the alloying for the small shop article, even for merely
curious this is worth the look.