I have an article from Brownells written by Guiseppi Forte, Master Engraver. Article number #076-200-388, but it did not come up on their site. I can't scan it at home, but Brownells will probably be glad to send it to you. He list four methods for a gray finish:
1. Hot blue first, then partial removal of blue to achieve gray (using phosphoric acid or 32% hydrochloric acid to do that).
2. Metal left white, treated with nitric acid to achieve gray. (mixed 1 part to 10 or 15 parts water. Then flushed with water, or club soda for a better finish)
3. Metal left white, then abrasive-blasted to achieve gray. Then black printer's ink is applied and baked at 275 for three hours. More methods given.
4. Electroless nickel first, the abrasive-blast to achieve gray.
These are just the titles of the four methods he describes.
That's where I got the idea to use cold blue and then take it down with 0000 steel wool to get the gray finish I desired, on my shiny receiver. The first coats of cold blue are gray, and not blue. I remember warming the metal with a pencil torch before cold bluing.
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