Friday, January 9, 2009


I managed to squeeze a few hours in in the studio today. I was thinking I might be able to finish the enamel piece in time to photograph it for the Enamelist Society show but no such luck. But I did get a number of pieces ready for the tumbler.

For those of you who are not familiar with the quirky properties of sterling, it is prone to a nasty thing called firescale. Firescale occurs when the copper in the sterling alloy is exposed to heat and air (during soldering and/or annealing usually) and it oxidizes. Here is how I understand the reasons behind the two traditional fixes for this issue:
The pickle removes the upper surface layer of the oxidized copper (in fact, pickle only eats copper) but unless one sands into the metal to remove the lower layers that still contain some oxidation, that oxidated copper will show up as a purplish discoloration on the silver. It does not EVER look good. If you sand the metal to remove the firescale, you must not heat it again or you will cause the copper in the alloy to oxidize again and you will have to start your cleaning process all over.

The other way to attack firescale is to anneal and pickle the piece until the pickle has removed all the copper from the surface of the piece, leaving a thin layer of fine silver. Over successive annealings, the exposed copper is oxidized. The pickle eats the copper, but not necessarily all in one go. It may take several heatings and picklings for the pickle to eat all the copper away from the surface of the silver to the point that when next heated, the copper is too far from the surface of the metal to oxidize.

If you use this approach, make sure you beef up your solder seams because solder is eaten by pickle faster than the piece will be eaten and it will evaporate under the torch some as well. If you have wimpy seams when you start your piece, you run the risk of the pickle eating through them during your finish work. Also, you must not sand the piece again because you will remove that layer of fine silver (although you will not then expose firescale, just sterling). This process leaves the piece with a microscopically (sp?) porous surface and it leaves the piece very soft. To work harden the piece and seal the surface, I tumble everything I do (pre-stone setting) with stainless steel shot for at least 18- 24 hrs. I don't like to sand because much of my work has texture and/or large flat expanses with elements on top and I don't want to create any dips from sanding the flat surface nor do I want to ruin my textures. And also, I really don't like to sand.

Both ways have their pros and cons. It's just a matter of preference really. One fabulous advantage to the tumbler is that it finishes chains beautifully. It polishes them safely, work hardens them and makes them more supple than any other method I know.

Here are some of the items I was able to get ready to tumble today. It's so nice to be close to finishing some work!!! Notice how white the metal looks. That's the unpolished fine silver.

BTW, I don't bother raising the fine silver on findings unless I've had to heat them for some reason. Notice I've connected the jumprings. You will be searching through your shot for hours to find those little buggers if you don't string them, hook them together or something.

No comments:

Post a Comment