REVISED (pics of actual AK Pistol Front)
okay here is my mix that worked perfectly! (UPDATED!!!!)
Safty First!!! Make sure you are wearing neoprene gloves and proper face/eye protection from splashing, whenever handling the acid. Also recomend wearing a respirator when dealing with the powdered chemicals.
I started off with:
4-6oz of 30-40% Phosphoric acid ("Behr #991 Concrete Etch" or "Klean Stip - Phosphoric Etch & Prep")
3 table spoons of Manganese Dioxide powder
a pack of '000' fine steel wool
1 gallon of Distilled Water
(pre mix the manganese and the acid into a glass jar and let sit for about 2 hours for the manganese powder to disolve as much as possible, 2 hours worked fine for me.) You can stir with a stainless steel spoon, or plastic spoon, to help keep the powder from setteling at the bottom of the jar.
Pour 1 gallon of distilled water into a stainless steel pot (pyrex or ceramic coated steel pot will work too)
add your acid/manganese solution to the water very slowly to try to keep splashing to a minimum.
REMBER ALWAYS ADD ACID TO WATER, NEVER WATER TO ACID!!!
Bring the blackish/brown solution to a low boil... when the solution starts to slow boil, slowly float a biscuit of steel wool (after soaking in and wringing it out in acetone, to remove the oil) and wait for it to disolve (4oz of 40% will eat about 1 biscut, 6oz will eat about 1.5, etc), keep adding pulled pieces until they stop disolving. Then let sit at a slow boil for 20 or more minutes. then you can turn off the heat and let the sediment settle, and you should skim out any uneaten steel wool.
once you liquid is cooled DO NOT STIR or AGITATE the LIQUID!!! You want only the greenish liquid, and to seperate the sediment from the greenish liquid. Carefully siphon the clear greenish liquid into another stainless steel pot (or pyrex etc...) or bottle and this will be your parkerization liquid. When ready to use the liquid pour it into your tank, make a note of where the liquid level is in the pot and bring to a low boil (~185F-200F) and when the soultion reaches that temp, you can add your items to be coated. As the liquid reduces from evaporation, slowly add more distilled water to bring the liquid to the level you noted, but no so quickly that it drops the temperature below 185F.
Now, you add your cleaned/preped/oil free (I used acetone) parts to the hot liquid, make sure they are completely submerged in the solutiuon (recomend suspending small parts in a stainless steel basket or suspended from a stainless steel wire), and they will fizz and give off CO2 gas, after about 10-20 minutes, your parts will stop fizzing (depending on the hardness of the steel it may take more or less time), at this point they are done.
You can remove them from the parkerization bath and rinse them off with hot water, and lightly rub off any buildup that might occur with a nylon brush. using an air compressor, blow dry your parts completely and/or bake out any remaining water. immediatly coat your items with any oil of your choice, (I have found that WD40 will evaportate quickly), I used 10W30 motor oil or cutting oil.
Let your items sit heavly coated with oil for about an hour, then you can wipe down and remove the heavy oil and coat with CLP.
My test pieces came out a beautiful dark charcoal grey/black in color and the finish was very uniform, deep and hard.
As you can see any brazeing will not take the finish, this pistol front was brazed at the front site, and where the gas tube was cut and reattached. Item was lightly sandblasted, and scrubbed with break cleaner, and then soaked for 20 mins in acetone, then dunked into the tank for about 15-20 mins till the light fizzing stopped. (harder and heavier piceces will require more time) Now, this unit will get scrubbed one more time to remove the oil, and will get a GunKote or DuraCoat finish to complet it.
FYI- Before dunking this in the tank, I did also plug the Breach, Muzzle, and Gas block opening, with corks to keep the solution from entering the barrel and possibly fouling the chamber and rifiling.
If doing larger items, proportionaly increase the amount of chemicles, or do several batches until you achieve the amount of solution you need.
(Results may vary)