Use Aqua Regia - the mixture is 2 parts HCl to 1 part HNO3. You'll have to mix it fresh for the day you want to use it. Starts breaking down and getting weak if you try to keep it premixed for more than a few days.

Marty

Good Question. Now my question is where does one obtain such chemicals, and is there some book available to instruct in all of the etching process. Thanks, Wesley

10% Oxalic Acid in water electrolytic is the best for 300 series stainless. 10g oxalic acid / 100 Ml of water. Etch at 6 -10V until desired structure is present.

Mr. Rogerio Lopes da Silva, Metallurgical Lab. Technician of Mackenzie University at Sao Paulo, recommends the following etching solution: a mixture of 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