Hey guys so I’ve been melting aload of my sterling silver scrap and pouring it into a buckle of water to create these flakes. Some of the piece have different colourations in them, seem to have orangey bits of copper wrapped within silver? (See attached pics) Is it possible that the alloy has split and now it is no longer .925 sterling silver? If I now recycle these flakes into something else might it not pass assay?
The melt consisted of purely .925 ear ring backings which had silicon rubber pieces inside so I melted it all together to burn out the rubber and make the silver useable for vacuum casting.
Is it safe to use this silver for casting now?
Any help much appreciated!
Unless you overheat the metal substantially, I can’t imagine how you could lower the proportions of the silver/copper alloy of sterling silver.
Have you put the metal in pickle? My guess is that what you’re seeing is surface discoloration. Pickle should remove that.
So in answer to your question, if it was .925 before, it should still be .925 now and safe to cast with.
Your pours came out in really big lumps. You can create smaller individual pieces by pouring the molten metal into water a little slower. It takes a little bit of practice, but isn’t hard to do.
Also, I prefer to pour into a deep container of water (sometimes I use a 5 gallon bucket) with an old ceramic dinner plate at the bottom. The ceramic plate catches all of the metal and insures that the molten metal doesn’t melt a hole in the plastic tub.
That’s great that you have so much scrap silver!!
There are lots of variables. They include: depth of the water, temperature of the water, height of the pour, speed of the pour, you can even pour through some sort of sieve or roll it off of a charcoal block to get little round beads. As for the color, I suspect that it will disappear in a concentrated pickle. You might have to heat it for a bit. The great thing about this process is, if you don’t like what you get, just do it over in a different way. Good luck…Rob
I agree that it would be hard to think of a scenario where you ended up with silver with more copper and less silver…that is, .920 or less rather than .925 or more. If you want a rough and ready test of whether you have sterling or not, you might try comparing known sterling, your unknown alloy and fine silver in a melt test. Sterling melts at 1640F and fine silver at 1761F…quite a difference…so if you took a small piece of known sterling, a small piece of the same dimensions in your unknown alloy and an equivalent piece of fine silver and played a torch over all three equally, you could see whether your alloy melted at the same time as the sterling…and you would certainly see the fine silver melt at a much higher temp.
If you got concerned about your alloy being under .925, you could always throw a little known fine silver into your ingot…you are not going to get in trouble for stamping .935 or .940 as .925 and the working properties are not going to be that different as to make a problem for you. The fraction 935/925 is 1.01 and 945/925 is 1.02, so adding 2% of fine silver would give you a good cushion if you are over-scrupulous, like me. -royjohn
In addition to what royjohn suggests, a piece of sterling that has been melted, turns a darker color when it cools. Fine turns closer to white…Rob
I have say that the photos do not look like fire stain, but like brass or gold, however photos can be deceiving. Give this a try. Mix a fresh batch of Sparex type pickle (NaHSO4, sodium bisulfate) , but use hydrogen peroxide instead of water. The H202 will oxidize any surface copper to CuxOx allowing the acid to dissolve the copper. This also works great to remove any copper flash if you accidentally use a steel tweezers to pickle an object in well used pickle.
Quenching molten metal will more often than not, leave a very thin surface discoloration with alloys containing copper. I agree with Jeff that the melt cannot be less than sterling in silver content, if you did not accidently contaminate it with copper in the form of filings or other dross. If melted in a strongly oxidizing flame, some copper will burn off into the flux leaving the flux brown with copper oxides. the result will be a higher grade of silver than sterling… “fire refining” involves the injection of oyxgen into alloy silver.,., fine silver will absorb 20X by volume its volume in silver… copper gets burnt off and left as copper oxide in the flux,. as the silver cools, it will exsolve the absorbed oxygen as “spitting siver” with large bubbles of oxygen forming… therefore your pour cannot have less than sterling content.
Hot pickle should remove the surface discoloration. NaHS04 (sodium bisulfate) should work well. The addition of H202 as suggest in the last post would also work but I don’t think that it would be necessary.
So far as doing melt tests to determine the silver content, looking up online, the phase diagram for the eutectic point of silver/copper would give you the precise temperature at which any copper/silver composition will melt at. A 28.1% copper to silver weight percent ratio melts at 780 degrees C or 1480 F… thiis is the eutectic composition and is the lowest melting point for any silver/copper alloy,adding either more copper or more silver to the melt raises the melting point… Eutectic silver/copper is unsuitable for solder as it has a gray color… solders can be made soft, medium, hard by progressively increasing the silver content away from the eutectic point to more silver composition. By using the phase diagrams, I made my own silver solders. The same applies to a gold/copper alloy which has a eutectic temperature near 50/50 atomic weight percent. adding more gold or more copper to the alloy increases the melting point. The eutectic compostion melts at 940C or 1742F…this is the lowest melting point for a gold/copper alloy composition.
Trimetallic alloys are a much more complicated beast with ternary points and planes in a 3D space corresponding to composition and temperature.
Sorry for the long winded discourse but those who know me, know that I’m into the science…
I like what everyone has to say… and at least one person appreciates the science behind it… thanks to all of you… I think these conversations are great teaching points for those who haven’t discovered it for themselves through reading and trial and error… great for beginners and advanced people alike…
@LukB83199 one thing that wasn’t
Addressed was the silicone and rubber
That was included in your melt and you
Decided you could burn off these
Inclusions. That may be what you see
Some silicone is similar to copper and as was suggested earlier when overheating
Some separation is possible.
The pieces of metal look very cool, I’ve
Taken some smaller pieces and soldered
A piece of round stock to the flat side and used it for part of a setting to hold a stone in place. … Steven