10 milliliters of nitric acid, 10 milliliters of acetic acid, 15 milliliters of hydrochloric acid, all of them concentrated, plus two drops of glycerine.
The following precautions should be taken when preparing and using it:
Use fresh, never store for a long time (that's why you should prepare a small quantity).
Discard when it takes an orange color.
Use with care, if possible under a ventilated hood.
Add the nitric acid last.
Inmerse the coupon for a few seconds to one minute maximum.
Sorry, I don't know where those reagents can be bought in the U.S.A.
Giovanni S. Crisi
Sao Paulo - Brazil
https://app.aws.org/forum/topic_show.pl?tid=2718I will add a personal note to this, mixing anything with nitric acid requires you to pay attention, wear personal protective gear and use a fume hood.