I successfully hardened it in my domestic oven after polishing,
then removed any discolouration with pickle.
confused me. I would think that putting a piece in an oven after
soldering would be the same as annealing it, which is softening,
not hardening. And wouldn't it make more sense to pickle after
soldering to clean the surface, then harden or soften, and lastly
polish? Or am I misunderstanding what you're doing?
Read the following article by Cynthia Eid:
Argentium sterling silver (and to a lesser extent, ordinary sterling
silver) can be hardened by a process called heat hardening or
precipitation hardening. In the case of sterling, it involves two
steps, firstly heating to a red heat for a certain amount of time
(preferably using a kiln) and then quenching at the right moment, to
freeze the metal particles in the state required, then secondly,
heating in a kiln to a lower temperature of about 230 degrees
Celcius (from memory so I may have it wrong) for a couple of hours.
If I remember rightly, this is to do with certain particles migrating
to the surface, which otherwise would take many years at room
temperature - hence using an oven to speed up the process. With
Argentium, apparently the first step is not needed, and you can just
use your domestic oven to effect the hardening process. The above is
vastly simplified and can be explained much better by any of our
Argentium sterling contains a small amount of a metal (well strictly
a metalloid, meaning it exhibits some metallic and some non-metallic
behaviour) called Germanium. Heating brings the germanium layer to
the surface where it bonds with oxygen to form germanium oxide. This
protects the piece from tarnish and is also harder than an ordinary
sterling silver surface. The germanium oxide layer will form at room
temperature, but heating accelerates its formation, and of course
the oven heating is also hardening the piece at the same time.
The temperatures involved in the hardening process, ie those of a
domestic oven, are nowhere near high enough to anneal the metal and
make it soft, and of course do I pickle after soldering. The
hardening process in the oven can cause some slight oxides to form
on the surface, which can then be removed by a brief spell in the
However, Cynthia’s article says it all much better than I can, but I
hope this clears up any misunderstanding.