We have just started using 960 Argentium Silver in our jewellery production (we have been working with sterling silver in the last 7 years).
We use Vacuum Casting, with Argon, we use separate crucibles for argentium, separate soldering boards - we tried charcoal, skamolex or just soldering on different supports in such a way that the part stays in air during welding (I have read here several posts that say that it should stay in contact with air so that germanium does its trick).
However, when polishing, the pieces develop some spots, some of them are even grainy somehow, some spots are granular, even in relief, as if the metal were not homogeneous (link to a folder with pictures and videos here) . We tried putting them in acid (vitrex) and then polishing again, it does not help.
Any advice?
Some mentions:
when casting, we used only new Argentium Silver, it was not mixed with old metal. We used borax as well (maybe we shouldn’t?)
also when casting, we respected the temperature recommendations, both for the metal and flask Flask: 540 580
Metal: 980 1000
when soldering, we tried both with a big torch or a very small, fine, needle tip one, it made no difference
we used new polishing compound and new polishing accessories (both felt, leather and buffer)
we used argentium solder, but, for example for earrings, the earring post is sterling, since it is difficult to find jewellery findings made entirely in Argentium, and when we do, the offer is rather limited.
we buy the 960 Argentium grain from an official reseller - the Legor Group, in Italy.
Please consider significantly reducing the flask temperature.
You seem to have very large as-cast grain size. The best way to eliminate this problem is to reduce the flask and/or metal temperature.
Let me know if you have questions. This is not an uncommon problem.
Question: Our burnout schedule ends with the kiln staying for 1 hour at 650 celsius degrees, then we start casting. The majority of our flasks are 10 cm diameter/18 cm in height. I understood by reading somewhere that each minute it stays outside, the temperature of the flask goes down by 100 degrees. So I kept them outside for one minute before casting (and assumed that this way they would be around 540-560 when casted, as recommended by the Legor Group). I never got this kind of texture with sterling silver, which we used to cast with 650 degrees flasks, and around 950 degrees the metal.
Would you suggest keeping them in the kiln until they reach 560 and after that keeping them outside for a minute? Could that be too low?
Investment is an excellent insulator. The amount of investment you have around the part cavity will determine how much heat is lost.
If you have a heavy (large) flask, the heat loss will be low at the center of the flask. If the parts are close to the outside of the flask, they can cool faster than the parts in the center of the tree.
Your flask is 10 cm x18 cm and contains about 2.5 kg of powder and water. 1.8kg is powder. This is a large and deep flask.
In my experience, it is more important that your overall treeing, investing and casting technique should be consistent all the time.
It is understood that light parts with a high surface area will solidify faster than thick parts with low surface area.
This implies the need to have lower flask and metal temperatures for “heavy” parts and higher temperatures for light and “airy” parts.
Are you casting parts that have the same thickness (weight) and size together in the same flask?
Parts that are similar should be grouped in a flask.
I would lower your flask temperature by 50C-75C and see if you get better results.
Heavy castings can tolerate significantly lower flask temperatures and the resulting casting will be significantly better.
