Christopher Tidy wrote:
What acid do you use, Igor? ...

As Iggy said - use muriatic acid, which is a low grade hydrochloric acid
(HCl). There is LOTS of info in the Google NG archives. Search RCM for
"muriatic rust".

Briefly:
- do NOT use it in the shop. The vapors WILL rust every exposed steel
surface!!!
- it is not particularly dangerous, except to the eyes. And the fumes
are very irritating to breathe.
- after derusting, rinse very well, in HOT water, and IMMEDIATELY oil.
The acid cleaned steel is very clean and will rust before your eyes
unless protected. I like to use wax - I keep a gallon can of paste wax
dissolved in paint thinner. I just dunk small parts & paint it on others.
- the acid will dissolve aluminum and zinc (galvanizing).

Bob