I much prefer OxphoBlue from Brownells.. It will blue thru a light coat of oil, it withstands abrasion and wear extremely well, and if given several coats will color extremely well. It is not as dark as some but lasts much better than anything else. Down sides include having to heat the part (usually) to get it to work well and the need to aviod contamination of the remaining material.. I use a heat gun to handle the heating chores (needs to be hot but not sizzling hot) and a spouted bottle to apply the material to a makeup patch held in a forecepts.. You need a clean applicator fairly often.. Follow the directions and burnish with steel wool between applications..
