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Casting Silver medalions


#1

I am trying to cast some simple medalions out of silver and suddenly
have a very strange problem.

I made several with little problem melting pure silver and 7.5%
copper in a clay graphite crucible which is much too large for the
project so I bought a couple of much smaller graphite ones.

I took some of the scrap and sprues and melted them in the new
crucible with a tablespoon of borax and after 3 pours, I have yet to
get one till fill the sand mold. It just does not pour nicely.

This is the same pattern that worked before.

What is very strange is that the parts have coatings in spots that
appear to be glass and extremely hard glass at that.

I suspect this has something to do with the borax but I thought I
read somewhere that this is the proper flux for silver.

This glass seems to be what is making it difficult to pour.

Any ideas? Could it have anything to do with the graphite crucible
vs the clay graphite?

Is a tablespoon of borax too much for 500 grams of sterling?

js


#2

The glassy stuff is the borax. I doubt that it is causing the
problems with the pour.

I do cuttlefish casting rather than sand casting, but the principle
is the same, in that you are not pouring into a heated mold, but
rather a room temperature mold, so your silver needs to be hot, hot,
hot in order to completely fill the mold before it solidifies. I
find that I need to heat the metal until the liquid blob appears to
be spinning around, and continue heating until the flame around it
becomes a bright yellow. I tilt the torch so that the flame heats
the lip of the crucible as well as the silver, so the silver doesn’t
cool as I pour it.

HTH,

Lee Einer
Dos Manos Jewelry
http://www.dosmanosjewelry.com


#3
    What is very strange is that the parts have coatings in spots
that appear to be glass and extremely hard glass at that. 

Is the glassy material green? I suspect it’s the borax alright;
I’ve made similar schmutz while mucking around with fusing. I found,
after the first very green and very glassy effort, that a little goes
a long way.

-Michael Balls


#4
 Is a tablespoon of borax too much for 500 grams of sterling? 

Hi Jack, Try using way less borax for the fluxing. 500 grams silver
is right around 16ozt so we are talking “pinch”. Like the bartenders
of old when the gold panners came in for a drink at the local saloon.
A drink would cost say a “pinch” of gold dust. Bartenders with big
fingers would have probably been hired first. But back to the
borax…just a small pinch. Watch for the surface of the melt to
clear and you are ready to go.

I took some of the scrap and sprues and melted them in the new
crucible with a tablespoon of borax and after 3 pours, I have yet
to get one till fill the sand mold.  It just does not pour nicely. 

Also you want to use some new metal with the old. A 50/50 mix
should work for what your doing.

Cast on,
Steve Slaughter
The Alchemist Casting Shop
Seattle WA 206-933-9255


#5

Jack,

the glassy coating is the borax. A graphite crucible reduces
oxidation. I never use more than a sprinkle in a clay crucible, and
none in a graphite crucible. It’s not so much a factor of the amount
of the metal, but the surface that is exposed to air. Way too much
borax. Is the “scrap” you are melting fabrication scrap or casting
scrap? It should be a 50/50 mix of previously unmelted metal and
casting scrap.

hope this helps
gail


#6

With regard to filling sand castings…
I have taken to pre-heating the sand mold to about 500 degrees before
melting my metal, and my success rate has gone up considerably.

–Noel


#7
Is the "scrap" you are melting fabrication scrap or casting scrap? 
It should be a 50/50 mix of previously unmelted metal and casting
scrap. 

I don’t have any fab scrap as yet because I have done very little
fabrication so far.

My “unmelted metal” is either fine silver from ingots or the same
blended with 7.5% copper.

I have been making the alloy and pouring the mold and the rest into
the ingot mold which is then remelted for the next project if
sterling is needed.

I still have mixed feelings about sterling vs fine and don’t really
have a good handle on why to use sterling for jewelry type stuff.

js