What changes parking to the greeenish color that is sometimes seen in WW2 guns? I know that it was not that color originally. I tend to remember that motor oil would do that or was it some other lubricant?

When I got my #4 MK1, it had been "sporterized", with the stock cut off, and refinished. Before I did a little restoration to it, it had a sort of greenish color to the barrel and reciever around the stock. Maybe its from linseed oil, or another wood-care product?

ETA- Is "Parking" the proper term, like "Blueing" for "Blued" guns? Not being a grammar Nazi, Just curious. You may get a better response with "Turning Parkerization Green". I was a little confused by the title myself.  

FWIW, according to some sources, it's due to the Park formula being weak when the weapon was dipped.

Coat your parts in cosmoline, wrap them up in one of those gun storage bags, stick the bag up in your attic and leave it for a year.

Never tryed it but it's been advocated on Culver's Shooting Page.

Look around over at jouster.com, the "green" parkerizing is a process of the original park reacting with oils and such over time..  Parkerizing is usually one of two types, manganese phosphate which is charcoal black and zinc phosphate which is varying shades of gray and "thinner" in depth..  

I've also read that coating in cosmoline directly after parkerizing (and still hot) can get the "aged" green park look quickly.  Never tried it myself.

Thanks guys. Heard you could use 90 wt gear oil, motor oil, cosmoline, and several other things but never found anything definative on what works best or at all.

Pretty sure the standard answer is long term storage in cosmoline creates the faint green tint to the parkerization

While age and oil affect the color, so does the original formulation of the park solution.

There used to be an outfit in the Arlington, TX (greater Dallas) area, Lone Star Ordnance.  I have been told they are trying to reopen.  Anyway, years ago I purchased a lot of small AR and other parts from them.

They specialized in refinishing M1 Garands, M1 .30 Cal Carbines, 1911's, etc.  They had done research and experimentation with solutions, and would duplicate the color or shade of parkerizing that came from each of the manufacturers.

Back to the oil... a great part of parkerizing's corrosion protection comes from the porous surface formed by the chemical reaction.  This surface holds oil like a sponge.  It is this ability to hold oil that helps in protecting from corrosion.

Anyone who has degreased a parkerized firearm has seen the change in color that results.  Ditto, burning the oil off the barrel by rapid fire.

So, it is partly the oil, partly formulation of the park solution.

A noted gunsmith I know used Havolne motor oil because of the green color. Applied it after taking it out of the park tank. They have since changed the color of the oil.