Tom is quite correct. Cyanide can give a nice hard outer surface just like bone and charcoal if the proper procedure is followed. Many older tools built by Starett etc used this process. Once I learned how difficult handling and disposing of the stuff was I pretty much lost interest in it as a viable process for me to use. Pete Mazur has used this process extensively in the past and is very knowledgeable about it. I do not believe he offers it currently due to regulations regarding it. You will likely get the best information from the company that is offering the service. I'll bet they could tell you if you will get a hard outer skin on mild steel using the process they use.

Firearms imports, consignments


[Linked Image from i.imgur.com]