I am confused about what the situation is. If it has been pickled,
why are there black crusty spots? That sounds like one of the
- it was not in the pickle long enough, or
- there is old flux stuck to the metal and the pickle was not hot
enough (or hot water can dissolve flux also)
As to the metal looking dull, that sounds like it could be a
description of what happens when something has been left in the
pickle too long.
This sounds to me like one of those mystifying things that happens
sometimes---since it has not happened to her before with traditional
sterling, I don't think that the hard water or body chemistry have
anything to do with it, and it does not sound like it has anything to
do with being made of Argentium Sterling, either.
It is hard to give advice, since the situation sounds so confusing,
but here's my best shot:
-clean off the black stuff somehow---either through hot water, hot
pickle, or abrasion (scrape, file, sand, or polish)
-if abrasion was used, heat for 20 minutes at 250 degrees to speed
up the creation of the germanium oxide layer
-brighten the finish, using one of the following: tumbler a brass
brush, used with soapy water for lubrication or Goddard's Long Shine
Silver Cloth or Long Shine Liquid Polish
I hope this is helpful.