Back in the 70's when Green River Rifle Works was operating in here in Roosevelt Utah, they came up with a formula for an acid browning solution that produced one of the finest end results I have ever seen. I got some of this stuff from Doc White a number of years after they closed their doors, and browned a couple of rifles I put together, but as all things tend to do my supply came to an end. This stuff was made from some pretty strong chems, in fact they are classified as industrial poisons, which means there is no way to duplicate it without obtaining a hazardous materials license. I say this because of the difficulty I am having getting parts to brown. It is very dry, and right now pretty cold, here where I live so the products on the market really need help, like adding moisture to the air, which given my space is really difficult. I have now tried three different products out there, did all I could to clean the metal beforehand, including sand blasting. With GRRW's solution all I had to do was bead blast the metal parts, make sure I didn't touch with bare hands afterwards, apply, and bob's your uncle a great deep rust brown. This was dead of Summer, dry season, no added moisture, two or three applications. With the liability problems with live with no days I know we will never see any product to equal it, unless I could find a chemist that would run me a batch....