I use a verticle tube tank with the ferric chloride etch in it.
I do the etch for each rust cycle.
Some seem to rust and card 2 or 3 cycles and then etch that combined color depth.
Try it and see what results you get.
Sometimes what works great for one person is a failure for another simply becasue of some unmentioned small variables in the process. There are so many.
I played with dunking the bbl alternately from the muzzle down to the breech down every other etch to see if that made a difference in anything. Thinking first in/last out muzzle end ech time might result in variance in color or etched surfaces.
Didn't really seem to make a difference.I use a very weal etch soln,,by my shade tree calculation probably less than 2%.
I dunk the bbl into and then back out of the etch tube just as fast as it can w/o being careless in how I handle the parts.
Then again as quickly to get the bbls under running cool water to flush off the remaining etch soln that still clings to the surface assisted by another carding this time with 0000 steel wool done right under and with the running water..
It can work that fast in loosening the oxide on the surface that you just built up.
(Coat the bores to prevent them from being etched each time,,I coat them over with plain shellac, a heavy coating applied with a swab on a cleaning rod..
It stands up to the boiling water and etch soln just fine. Even then I apply an extra coatin at around cycle 8 just for good measure.,,figuring it usually takes 15+ cycles to get a decent damascus finish. Sometimes less, sometimes more.
But the process just by it's methods of etching keeps removing part of what you've done each time, Soi the build up of color is slower than with straigh out bluing or browning.
As Keith points out it's only the difference in how tenacious the grip of the oxide coating is on the bbl that prevents it from being loosened and then removed during the etch & card process.
The oxide binds to the iron a little more than that of the steel in the twist pattern, so you (hopefully) end up with color remaining on the iron portion and then the steel part of the pattern cleared of color.
