plating, anodizing, & finishing Q&As since 1989
History of Parco-lubrite, zinc phosphate, and manganese phosphate coatings
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Q. Thomas, can you point me to where I can find the difference in the coating weights between the 2 and 5, and possibly the TDSs for both?Russ Rohloff
- Fort Collins, Colorado
November 1, 2022
Ed. note: Thomas' reply was from nearly 10 years ago, but we'll see if his e-mail still works :-)
Closely related historical posts, oldest first ...
Q. I'm trying to get a history, including time line, of the use of Parco-Lubrite, zinc phosphate and manganese phosphate, especially before and during World war Two. This is for research on the finishes used on certain U.S. firearms produced during the war. I have seen the data published on Wikipedia, https://en.wikipedia.org/wiki/Parkerizing. Does anyone know a source of in depth history on the use of parkerizing?
I also see that Parco-lubrite is currently a manganese phosphate solution, yet I'm pretty sure it was a zinc phosphate solution during the war. Does anyone know when the composition was changed?
If you know of a book that explains this in detail, I would be glad to purchase it. Your help is much appreciated.
researcher & writer - New York
January 23, 2009
A. Hi, Chris. I tend to believe Parker-lubrite was manganese based from the very beginning. I am looking at a 1939 book "Protective Coatings for Metals" by Burns and Schuh, which reports " ... in 1918 it was found by the Parker Company that the character of the coating was improved by the use of a solution of primary manganese phosphate. In this process, which came to be known as Parkerizing ...". I have some other references asserting the same. Sorry, I don't know offhand where the "Lubrite" term arose.
Without research I can't dispute the Wikipedia assertion as to whether or not there was a conversion to zinc phosphate during the war. My mentor Joseph Mazia was the director of the metals development lab at Frankfort Arsenal during the war, and later an employee of Parker+Amchem, and would have been able to give you the accurate and full history. Unfortunately he has passed away.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. From what I understand, the word "parkerizing" is a generic term for a phosphate coating. It could be zinc or manganese phosphate. The Parker Rust Proof Company filed for use of the trade name "Parco Lubrite" in 1940. According to the Wikipedia article, The Parker Company received two patents. One in 1938 for a phosphatizing process using zinc (which was more readily available during war than manganese). The second was granted in 1942 for an improved zinc phosphatizing process utilizing copper and a chlorate to make the process more economical.
While I have found nothing to show that Parco Lubrite was a zinc phosphatizing process during the war, it would seem that if the Parker Company was putting all that time into developing an economical zinc phosphatizing process, then that would be what they were selling/producing.
My primary area of interest is in the production of M-1 carbines during World War Two. There were ten different manufacturers of the carbine. The color of the phosphate finish varies among the producers. For some producers the finish is a light silvery gray that I'm sure is a zinc phosphate finish. Other producers have carbines where the finish is typically darker and some have a very greenish tint. Did all these companies use a phosphate coating that utilized the improved and economical process that was patented by the Parker Company in 1942? It would seem that the most economical method using the material (zinc) that was most readily available would be the on to use.
If all companies were not using the improved zinc phosphatizing process patented by the Parker Company, then what were they using? Does anyone have the names and companies that manufactured other phosphatizing products during World War Two? I have only seen the term "Parco Lubrite" in reference to the phosphatizing process on ordnance and carbine manufacturer documents of the period.
If all the companies were using Parco-Lubrite, be it zinc or manganese in composition, why all the variations in the color from a light silvery gray to a black?
There's one more thing that I'm curious about with regards to the color. Many World War Two firearms have a phosphate finish with a greenish tint. Many people have conjectured that this is caused by years of storage in Cosmoline. I have my doubts about this. There are two possible ways that I think the greenish tint is on the finish. First, if the finishing process used was the improved one patented by Parker in 1942, it would have copper in the solution. Could there be enough residual copper in the finish to cause some greening through oxidation over time? The second possibility lies in the chromic acid rinse. Could the chromic acid combine with the zinc to form a greenish color? I know that zinc chromate primer is green. I again thank you for your time.
- New York
A. Parkerizing is nothing more than a trade name for phosphate coating, just as Kleenex is a trade name for tissue.
Parker very aggressively advertised and promoted their products, to the point that "Parkerizing" was included in military and commercial specifications and on drawings.
As these parts were sourced through various sources over many years, some of them may have used Parker processes, and others used whatever phosphating process they had on hand. Some were proprietary, and some home-brewed.
I have myself processed parts which called for "Parkerizing" with both zinc phos and Manganese phos, none of it using Parker materials. Customers accepted this work just as though they had asked for a Kleenex and been given a Scott tissue.
As to color, zinc phos is usually light gray, but under some conditions it can be more nearly charcoal, and if chrome rinsed, may have a yellow or green tint.
Manganese phos is normally very dark gray, perhaps nearly black, but is sometimes charcoal. You may not be able to tell visually between a dark Zn phos and a light Mn phos.
In addition there can be a large variation in grain size in either process, and this, along with the visual difference between thin and thick coatings can make a significant difference in appearance.
Some specifications may call out "Parkerizing" and nothing else. Other specs may include requirements for coating weight, grain size and color.
Given the history involved, it is not surprising that "Parkerizing" done at different places and different times is different in appearance.
Is "Parkerizing" only that coating which is produced using Parker chemicals? Or, is Parkerizing any phosphate coating which serves the intended purposes of providing a low reflective surface which will absorb rust preventives.
It's the Kleenex versus bathroom tissue question, and you can argue either side ad infinitum.
And then there's the Thin Dense Chrome question, but I digress.....
Jeffrey Holmes, CEF
Spartanburg, South Carolina
A. Try old Angiers book on bronzing of firearms
"Firearm Blueing and Browning"
[affil. link to book
on Amazon] -- According to that book phosphate finish is somewhat older -- there you can find some early variants of process.
1906. Cosletts patent (zinc phosphate based)
1911. Richardsons patent (manganese phosphate based process).
Iron phosphate based processes are probably even older (late 19th century).
1929. German proprietary process(IG Farben)
According to W.Machu:Nichtmetallische anorganische ueberzuege (Nonmetallic inorganic coatings),Leipzig 1948.
Hope it helps and good luck!
- Cerovski vrh Croatia
A. I was a 35+ employee of Parker Rust Proof Company (name has changed with owners) presently retired. Was hired as a Chemist upon graduation of Missouri University. I was in upper sales management prior to retiring, and have used both systems in commercial installations. Parco Lubrite 2 (operates on the iron side Fe+2) gives heavy coating weights compared to Parco Lubrite 5 (operates on the NO2 side) no ferrous iron in solution.
Both coatings could be burnished for bearing surfaces. Coating weights can be reduced and/or refined by utilization of a conditioning agent prior to Phosphate e.g., Parcolene M. Some operational nuggets are given in this condensed response; should other information be required please ask me further. Individuals with knowledge concerning these pretreatments are becoming limited due to R&D efforts being focused in different more profitable areas and [loss of acquired knowledge] of personnel. The chemistry of this MnPO4 is very unique and I find it quite interesting regardless of profit margins.
- Shelby Township, Michigan
June 14, 2013