Hydrochloric etc

I was wondering if old hydrochloric is still ok to use if its
still in the original container unused? What can I do with it
and what and how can I use and find more info about acids and
their uses in jewelry making field, etching, finishing
texturing…you all helped me alot when I asked about bombing a
while back. How do I make my own gold testing solutions or wher
can I get the supplies and recipies etc…

Rael Fine Jlrs