JSeery, could you elaborate on this a bit. Thanks!
Yes, but I need to look it up it's been a while. I will post some information. The end process it to place the bolts in hot oil. Variations in the process gives you from gray to black finishes.
This is rough from my notes (this is not original with me!!).
Heat water (I use distilled water) to between 190 and 200 degrees in a stainless steel pot, then add Manganese Phosphating Concentrate. Do not mix first and then heat, add the concentrate to the hot water.
Manganese Phospating Concentrate can be found at Palmetto Enterprises (
www.palmettoenterprises.net). Palmetto offers it in five gallon buckets, quart and pint sizes. Mix it in a ratio of 14 ounces concentrate to 128 ounces (one gallon) water. This activates the phosphating chemical reaction.
Zinc Phosphate can also be used, but Manganese seems to work a little better to get a darker gray appearance. There are also other items that can be added to the mixture to darken the color. The Manganese phosphating process will turn parts to a dark gray finish.
Parts need to be clean, grease and oil interfere with the phosphating process. Remove grease and oils with an alkaline cleaner, which includes Easy-Off Oven Cleaner. Also need to remove rust, etc. You can also glass bead/bead blasting parts. Etching the metal allows the phosphate to chemically bond. Different acids can be used to remove rust and condition the metal, but you need to take it easy as they also remove metal for the parts.
Don't touch the parts with bare hands or use cleaners after sandblasting as this will leave a residue and create a spotty or streaky finish.
Submerge each part in the mixture using rubber gloves or stainless steel or rubber-coated tongs. A rubber-coated magnet can be used for submerging and retrieving smaller parts.
Once submerged, bubbles begin to form on the metal and rise in the mixture, similar to dropping an Alka-Seltzer tablet into a glass of water. This fizzing action is phosphating the metal. It is a good idea to rotate the parts every few minutes to get an even coating.
Leave the parts in the bath for 8 to 10 minutes total, even though the fizzing has stopped. This promotes a slightly darker finish.
When removed rise the parts well in water, then dried with compressed air.
You can spray parts with WD40 application immediately after the phosphate bath. Wipe dry and repeat this step three times to ensure all mineral salts are removed. I think a better method is to dip the parts in heated motor oil, SAE 30 straight.
