Post Reply - More Scans of The Green Finish On M1 Carbines

   Green Color,
Years ago I had tossed around the idea of the use of Zinc Chromate Green in a reduced liquid form being used as a tint in the 1-after park 2-after rinse 3-Chromic Acid Dunk. Since the PDF (BELOW) mentions tint and I know Zinc Chromate (As a tint) can work in the temperature ratings that either Type Z or M phosphate is heated to.
Also since Zinc Chromate was already in use by the DOD on aircraft and marine use.
This link will give you a little info about Zinc Chromate and some of the colors and dyes in use pre-WWII:
http://www.colorserver.net/history/history-zinc-chromate.htm

After either a Type Z or M Parkerizing a after park neutralizing / rinsing is done. A Chromic Acid Rinse was then used as a sealer to provide additional corrosion resistance. I used to find it in MIL STD MIL-P-16232F in paragraph 3.2.5. But can no longer find it. Believed Superseded, but from my notes I see that DOD-P-16232 F appears to contain the same Specs to Z or M phosphating per the DOD requirements.

You can download in a pdf from the link below. Click DOD-P-16232 F or the Orange Download File- 74.21kb: http://everyspec.com/DoD/DoD-SPECS/DOD-P-16232F_10390/ ;
Then find 3.2.5 Stage 4 for details on the Chromic Acid Rinse. 
In this PDF are Specs and ratios of how much chromic acid (Flake) to use per liters/gallons of water, temp ranges, PH levels to maintain... etc.

After the initial parking and after park neutralizing / rinse were done. This is the next step required by Ordnance, the Chromic Acid Rinse used as a sealer to provide additional corrosion resistance.

11+ years ago much of this information was shared with me from 2 long time CC members.
They added this to the conversation-
"In an in-house newsletter published by Inland during the war there is a picture of a factory worker dunking assembled barreled receivers into a tank of sealer. The sealer would have been the Chromic Acid Solution. Too long of an exposure time or too high of a concentrate of H2CrO4 (Chromic Acid)  imparts the green tint to the phosphate coating. Too weak of a solution due to dilution or PH level will impede the green tint. Nothing spectacular just simple chemistry at work."

When asked if matching original finish was possible, one replied:
"It has been done using the same solutions, or as close to the same as possible using available period data and MILSTD procedures used today. After some trial and error the result was an olive green tint to the zinc phosphate finish."

I'd assume depending on the makers strength of this solution vs others is why we see some  greener than others. Depends on when it was treated.... fresh bath vs older bath ready to refresh. Keep in mind these tank solutions were kept track of for temp, ph, solution strength, mix ratio etc. They were inspected and logged.

I had 2 bad barrels cut to multiple ~4" long lengths each to experiment on. After trial, error, time and $$ that green tint was achieved that could not be washed off with Denatured Alcohol or any other product I could find.... Unless it was something caustic enough to break down the actual Park like Muriatic Acid. That 'Formula' is tucked away in my safe...... 

Charlie-Painter777