A History of Zinc Chromate

When I worked at McDonnell Douglas in the seventies I got word that a whole shipment of many cases of Zinc Chromate spray cans had been bounced by the incoming inspection folks at the receiving department. It got sent to a local salvage store.  The only thing wrong with it is that it did not meet the MDD color spec- otherwise it was fine. Since I was building a 1:1 scale homebuilt  at the time I bought a whole box of a dozen cans!  Lasted for years!

Yep, even airframe mfgs use spray cans for minor touchup work!

Very interesting BlackSheep, after reading that, when directions state the use of zinc chromate, the modeler could paint that structure almost any color and be correct.

Thanks, BlackSheep!  Extremely interesting!  I've noted color variations in photos of WW II aircraft and wondered if it was the quality of the photo, actual variations in the Zinc Chromate color, or, perhaps, fading.  I guess the answer is possibly yes to each of these.  But, now I feel a bit more "justified" in experimenting.

Thanks for posting BlackSheep - very interesting. I normally use a green colour for zinc chromate, but think i'll vary it with some yellow too. Always nice to have some bright colours on military aircraft.

I've been inside a B-17 and a B-25-  the color was definitely green.  But I'm sure there were other variations on the yellowish side as well.

Thanks for the reminder.

I'd read this article several years ago but couldn't remember where.

Chuck, just to point this out if it helps any. The Greens and Red/Salmons were the variations. The stuff that was painted on as Green or Salmon started off as Yellow, then had tints added to them for various reasons. Black was added to the Yellow to get the green, and the resulting shade depended on the person doing the mixing. Indian Red was added to the Yellow and that produced varied colored Salmons.

One other tidbit,,,,,to modelers we need to consider this as a paint color,,,,,but, it wasn't a color in real life, it was a coating (still used on the Phantom, in fact)   Old aircraft often got the Yellow painted on the parts first, then the Green was painted on to show that a second coat was applied.

And Interior Green was a completely different thing, an actual paint color, and much more uniform in color because it came from factories that made that color, not mixed from a stock with tints added.

Because of the US method of applying two coats,,,,,,,almost all of the Warbirds we tour will have either that second Green coat of ZC or a coat of Interior Green paint. (except for the Bronze Green, of course)

Rex

The zinc chromate was a primer that was pretty much in the form of a paint, as opposed to something like Alodyne that was a thin liquid chemical that was sprayed or brushed on, or the part was dipped in, and then the residual washed off.  Those coatings actually reacted to the metal chemically, as opposed to adhering to surface like a paint.  Now, I have heard that the chromate actually etched the surface a bit, but there was a vehicle and pigment just like a paint, so it was sort of fish and fowl at the same time.  The conversion coatings were extremely thin compared to paint.  The conversion coatings were somewhat like steel rusting, but the chemical produced was insoluble, like some of the metals that form an insoluble coating just from air exposure.

yes, it was a paint as you said. I didn't say it wasn't,,,,I said it wasn't a paint color like it is for our models.

And for another article that builds upon this information, look here.

http://www.ipmsstockholm.org/magazine/2004/01/stuff_eng_interior_colours_us.htm

Awesome, stik! Thanks for the link! Got that in favorites for later references. :)