If anyone is interested in blue - browning - pickling - etching - matting - derusting - denickelling and phosphating, I highly recommend this book with hundreds of recipes ... Firearms Bluing and Browning, by RH Angier, 1936
From another muzzle loading book source, I found the most beautiful butternut brown, browning recipe that I made and finished a Hawkins Rifle with. The formula, called the Rueben Harwood Brown is:
Nitric Acid - 1/2 oz
Ethyl nitrate - 1/2 oz
95% Alcohol - 1 dram
Copper sulfate - 2 drams
Tincture of Ferric Chloride - 1 dram
Rain Water - 1 quart
Mix in a dark bottle, cork and leave to amalgamate for one week.
PS: Rueben Harwood invented the 'Hornet' cartridge