Barrelbrowner,
I think Miller is right about the black/white damascus pattern finish. Give your tried and true process a try first, with the simple addition of boiling after the rusting.
After reading all the material and articles by several people and attempting this myself, I will say that some points were still unclear to me and it took a good many attempts over a few yrs for me to discover what process basics are needed. While I have only accomplished it on a sample of a barrel, I found a few things below.
1. It finally struck me that the etch bath of ferric chloride needs to be diluted quite a bit. This ratio/strength is unclear in all the material I read. I started with a 40% strength FeCl circuitboard etchant. This is the "full strength" of the commercially available circuitboard etchant. After messing with this over a few yrs, leaving it alone after a number of failures and coming back to it, I finally figured/tested to arrive at a 6 parts water to 1 part commercial circuitboard etchant (already diluted to a 40% strength). This is probably the most important thing that needed clarifying to me.
2. Approach the process just like regular barrel blacking/blueing. Use your favorite blacking process (rust, boil, card (RBC)). I liked doing three RBCs to get a good dark coloring on the barrels before doing the first etch and wet carding, then another three RBCs, etch & wet card. Then 2 RBCs followed by an etch and wet card.
3. The etch time is measured in seconds. About 5-10 seconds in the diluted ferric chloride is all that is needed, followed quickly by a flooding water rinse and the wet carding with 00 grade steelwool.
4. don't forget to neutralize. Baking soda or other similar in solution of water was suggested.
Here's my coupon after attempts over a few yrs and finally success. The coupon is a very fine damascus.
