I did it and am pleased with the results on my 1879 Parker D2. When I get it all back together I'll post pictures. After realizing my water was too acidic (hard) I went to distilled. Today I etched after 5 rust cycles and 4 carding cycles over a period of 3 days. The surface was a nice deep black. I brushed on the etchant and the contrast started popping out. When I thought it had gone far enough I washed it down with the hose - mistake. Almost as soon as I did that my barrels started turning GREEN. I realized that it was my well water and soaked them with distlled and etched again quickly. The etchant removed the green, then I covered the barrels with baking soda to stop the reaction. They have turned a bit darker, but still have nice contrast. I figure the finish will wear-in nicely and a perfect redo would look a bit out of place on a 130 year old gun. This was like baking a cake over 3 days, you really have to be vigilant and pay attention to the process. I have another set I'll start again soon. These barrels started with no finish at all and although I know what parker D2 looks like it was fun to watch the pattern pop out. Thanks again to you guys who share your hard-earned knowledge.

Please post some pictures when you are done. Lots of fun when you get it right.

If your water is acidic,I believe it is soft and would be below 7 which is neutral. You can buy PH strips to test it.

Acidic and hard are diferent issues. Acidic is pH and will cause problems. Hard is contamination with Ionics or "hardness" commonly calcium carbonate and Manganese depending on where you are. Hardness or Ionics also cause lot's of problems. If you can't make deionized water then Distilled is your next best bet.

Ed,
What rusting solution did you use and what strength FeCl4 solution?
Congratulations