Weird that no one has commented on this.
If someone does decide to try it, my opinion is that it is of worth to do so. The technique is also in an old book from the 1930's that I have on barrel browning and bluing (I forget the author).
What is not specific in either book is the ratio of copper sulfate to water. In Treadwell's book it calls for "two mugs" of copper sulfate, but no specific mention of the volume of water; citing enough to cover the barrels.
Additionally, the duration of the soak is vague. Treadwell calls for 30 minutes, and I don't recall the other book mentioning duration.
I can tell you that the process immediately starts to expose the pattern, which it pretty neat to see. In my case, the ribs especially responded with excellent contrast. The barrels will be coated with a dark salmon colored sludge, which will hose off. It is unclear whether they should be rubbed or not while rinsing, of if they should just be left to dry without physically contacting them. During my first attempt, I gently rubbed with paper towel, and this removed more of the color than I would have hoped. Next time I'll rinse and dry and see what happens.
Because of the color having been diminished due to rubbing, I did another quick dip. This was not a good thing to have done. When I carded the barrels later, there was a noticeable texture. This required that I polish the barrels again and start over. Thankfully, the texture was not significant enough to require the use of a file. I don't know if it was the solution ratios or the duration of the soak that caused this.
I'll be trying again. I like that is has historical applications, and if it makes composite barrel work a little easier, great.
