What does it mean to "parkerize?"

Hi,
The process involves suspending the parts in a hot (about boiling temperature) phosphate bath for around twenty minutes, then rinsing and applying a lubricant. The parts have to be clean and oil free. The phosphate solution probably varies, I have seen a recipe that calls for: phosphoric acid, distilled water, powdered manganese dioxide, and iron filings. The chemical process etches the metal and forms a phosphate coating on the part. The finish is durable and non-reflective(light to dark grey). Precision parts probably should not be done because of the etching and phosphate build up. There are kits available to do this (or something close to it) at home. Brownell's and others sell them.
Regards, Greg
 
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