Hello James ! @jamesb
I was hoping that you would respond to this. I wanted your thoughts on the subject. Since you and I both have been around many full sized "Warbirds", we have seen exactly what I'm trying to describe above in the various colors that were used.
You are spot on the money with your assessment about ZC being painted over. I am certain that the US Army (and Navy) had specifications that required the crew compartments to be painted in specific colors. I remember reading about Bronze Green, Interior Green, and Dull Dark Green as some of the colors that were specified. This is a stark change from what was required from only a few years earlier when cockpits were painted in an "Aluminum" color from the factory. Apparently besides the fact that you don't want something shiny in a combat zone, the crews were making complaints about safety hazards that were caused by glare from the shiny aluminum surfaces inside the cockpits.
So something had to be done...
To my knowledge, Zinc Chromate was used as a corrosion inhibitor and as a means to keep various types of metals from having an interaction between them. Unfortunately ZC doesn't seal a surface as good as a regular top coat color does. This is also part of the reason why they specified the interior crew compartments get painted to act as an additional protection.
Please keep in mind that these planes were not expected to survive for 70 years after they were built. A safe bet would be that an airframe with over 10,000 hours was unheard of at this time. These planes were considered "expendable".
Most people don't realize this, but placing two dissimilar metals next to each other causes a very small electrical voltage. It's how batteries are made too... This voltage can cause corrosion which is not what you need on a wing spar, or anywhere in an aircraft's structure.
This is part of the reason why Zinc Chromate was made. It sticks to aluminum. Some primers will not and simply peel off after it dries. It has been referred to as the "Galvanized coating" for aluminum because of it's properties, even though it's not galvanizing...
Here is some information that our very own Martin posted some years ago when he was doing research on the subject. A lot of information has been written and is published over at this website. It's called IPMS Stockholm and it has a wealth of information posted there. It's definitely worth looking at if you have any curiosity on the subject.
Interior Colours of US Aircraft, 1941-45, Part I
Granted this is a subject that the information changes as more research is done, and more documentation is revealed.
Here's what Martin had to say about the P-38 cockpit colors back then. This is specific to the earlier planes.
This next caption is what Martin wrote about the Zinc Chromate color itself...
Then he talks about another color that I didn't realize existed until about 10 years ago. It's called "Bronze Green".
Various cockpit green colors are explained...
as is Dull Dark Green.
Here I cropped it down a little so it's a bit easier to read. This is about the various "cockpit green" colors. I wish I knew about this stuff 20 years ago... Prior to that everything I built had "Interior Green" as a cockpit color. But I suspect I'm not the only one...
Speaking of Interior Green... here it is.
Now I can't wait to see what Dana Bell has written about the subject, and I'm more than anxious to see the color pictures of Glacier Girl as it was removed from under the ice.
I'm hoping that you continue to follow along with me on this journey, as I'm sure I will have more questions to ask you about this subject. Your knowledge about colors, lighting and photography will come in very handy as we go down this road.
Thanks again and I am glad that you decided to order the book too. I think it will be "enlightening" for both of us.
I can't wait. But I have too.
As always,
Comments are encouraged.