Hello, my name is Pablo, I am from Argentina, in this country
there is not good flux for soldering silver, all they crystallize
If you can't order flux from one of our U.S.A. suppliers such as
Stuller or Rio Grande, you can make a flux yourself that will work
OK, but it's not quite as good as the kind you buy. First, you need
to find Borax. Grocery stores carry 20 Mule Team brand borax in their
laundry products. Potter also use it in their glazes, so if you know
a potter, perhaps he or she could spare some. You will need to grind
it very fine with a mortar and pestel, which is like a small version
of the old tool used to grind corn for flat breads. (I see your
English is quite good, but I can't know how large your vocabulary of
English words are). I don't know much besides English and French.
Anyway, once you get the borax ground fine, mix it with water to the
consistency you prefer. Let us know if you try this, and whether it
works for you. I'm sure others here will offer more suggestions.
Best of luck.
David L. Huffman