That is a VERY good link. Covers most everything, but of course they could not cover all the time and subsequent rustings/cardings/boilings, though they do mention them.
Back in the 80's a retired Marine Major brought a cheap Belgium Damascus double barrel into the shop that he wanted work on. I always got the call to "work on anything OLD" and the Major and I knew each other personally from NSSA and other activities. When he pulled the gun out of the case, the barrels were "Crusty Rusty." When I saw that, I said, "You are NOT going to shoot this are you?!!" He chuckled and said he was not, but he wanted a gun to show Hunter Education students what Damascus barrels looked like. However, you could not see the pattern for the crusty rust and that was the problem he wanted corrected. OK, if you are not going to shoot this, I can definitely do some things to this for an "Example Gun."
We walked back to the Bead Blaster and I reduced the pressure down and then back up to where it JUST took off the crusty rust to bare metal on about 3/4" of length of the barrels. When I pulled them out of the Blast Cabinet, the Major said, "But you can't see the pattern!" I replied, "Sir, forget about being a shooter for a minute and think back to your Ordnance days. (He was a Mustang Major.) I am not done!"
Then I put on a pair of the heavy rubber gloves we used for hot bluing and went over to small/long tub of Muriatic (Brick Cleaning) Acid we used to "strike" the surface of the SS Sniper rifle barrels before bluing. I wiped some acid on the now bare metal and let it stand for about 15 seconds while I walked to the deep sink. When the acid had JUST etched the barrels enough to see the pattern, I flushed them with hot water. The Major started to reach for the barrels, but I whisked them away and told him I was not done.
Then I grabbed my bottle of Birchwood Casey Hot Brown solution and the acetylene torch and browned about 1/4 of the length of the barrels near the "crusty rusty" part. I put just enough of that solution and heated it so that part of the barrels were brown and you could still see the pattern. The Major began to reach for them and I said, "Sir, not YET!"
Then I took the barrels to my bench and used Cold Blue on the last 1/4 length of the barrels near the muzzle. Three or four coats got them to a decent and rather flat blue. The Major looked at me and I just shook my head no with a grin on my face. Then I carded the crusty rusty and the area of the barrel I had browned with steel wool and oil. Then I gave the barrels a good coat of "Rust Veto" penetrating oil and wiped them down. Then I pulled out some car wax and waxed the barrels and wiped/buffed that off with a terry cloth rag.
THEN I gave the barrels back to the Major and told him the barrels now showed just about any condition that Hunter Ed students may see Damascus barrels in - from Crusty Rusty to Brown to Bare Metal to Blue. He was delighted and used that gun for many years to teach Hunter Ed students.
Of course I would NOT have used a bead blaster even on a low setting for a set of Damascus barrels that one would actually want to shoot. Too much risk of "blowing through" any soft spots.
Gus
