While I'm waiting for it I have a side question: I read online
that the maximum number of forging/annealing cycles for sterling is
5, as opposed to unlimited for fine.
It just goes to show that you shouldn’t believe everything you read
on the intertubes…
The issue with over annealing is mostly that too frequent annealing
will give you more grain growth than you may wish… Metal with
larger grain sizes isn’t as strong. So the answer to your question is
basically, anneal the sterling when it needs it. If it’s become too
hard to work, or is in danger of fracturing or splitting, etc, then
anneal it. There is no hard and fast maximum number of annealing
cycles. The metal does not remember how many times it’s been
annealed. It only “knows” it’s current state. It doesn’t keep
count… If that state consists of highly distorted and stressed
crystals, then annealing properly will allow those deformed and
stressed crystals to break up into smaller new crystals without that
strain and distortion. This new structure, with more, smaller, and
more homogeneously mixed crystals is stronger and better for most of
our uses.
Now, there are also caveats, but these apply whether annealing once
or dozens of times. When you anneal the metal, especially if in air
without protection, you are oxidizing some portion of the copper,
possibly giving surface layers, after pickling, of first, fine
silver, then layers with imbedded copper oxides. That layered
surface, giving you what we call fire scale (the surface black oxide)
and fire stain (the reddish tinted silver/copper oxide mix of the
metal under that scaled surface). These are not something that
additional annealing helps, but rather, can make worse, and are
changes you normally don’t want (exception, when doing reticulation,
that structure is what makes it work). That incorporation of copper
oxides into the surface can make the metal weaker, more prone to
surface cracks in working, as well as giving major problems when
finishing, as the oxide containing surface layer is a different
color/appearance from the clean sterling under it. Also, annealing
without protection from oxidation like this means you are, over
repeated annealings, reducing the percentage of copper in your alloy,
so it becomes higher in silver than 925/1000.
As well, if you anneal for too long a time, or at too high a
temperature, after your metal recrystalizes, then those crystals
start to combine and grow into a structure with larger, fewer
crystals. Normally, you don’t want that (exception, if you’re doing
something like etching the metal to show that crystal structure, and
want the larger, more decorative crystals). The lesson there is that
proper annealing technique, ie protecting the surface as needed, and
not annealing to too high a temperature, is what’s important, not
some supposed maximum number of anneals.
One rule of thumb with sterling silver is that you can reduce the
metal by 90 percent before needing to anneal. That’s more a
suggested maximum than it is some amount you must reduce the metal
before annealing. If, for example, you’ve reduced it by only 30
percent, but it’s become too hard to do what you’re trying to do,
don’t feel you must continue just to get a higher percentage of
reduction. If you need to anneal it, then do so.
Peter