I need to do some silver etching with Nitric acid. I have found a few sites online to make the purchase, (the shipping is a tremendous amount of the cost due to its hazardous nature), but what I have not figured out is what concentration I need for my etching purposes. I can buy the concentrate, which is 69-71%, for a relatively reasonable price.
I personally mix mine to approximately 25% strength. I didn’t like
the cost of the available nitric acid and its shipping costs, so I
purchased mine from a hydroponics website. It was sold as “Nitric
acid pH down”. That confused me at first, as I thought it was some
sort of mixture of nitric acid and sodium bisulphate (as sodium
bisulphate is often sold as “pH down”), but it is just a 38%
solution of nitric acid, which I then dilute down to 25%. There were
no outrageous shipping charges, and it was a reasonable price itself.
Even better than nitric acid is ferric nitrate, which comes as a
solid, in granular form. It etches more cleanly than nitric acid,
which tends to be too aggressive and produces a really blotchy etch
with no clean details.
It sounds like you already know how to achieve the required dilution
(if you do indeed want to use nitric acid rather than ferric
nitrate), but if help is needed to calculate diluting from 70% to
25%, for example, then just ask offline and I’ll give a detailed
breakdown (I’ve been criticised for giving such advice on forum in