As I recall, Dr. Gaddy found the "stuff" in the layers to be very complex and not necessarily uniform. The layer thickness is important to the color, not the composition. Differing compositions can/do create equal thickness layers which cause the same color. Given colors are not associated with given compositions, to my knowledge.
I agree that strong basic (high Ph) would likely attack CCH.
Interesting discussion!
DDA
The fact that different compositions can cause the same color is because the colors are optical interference colors and not due to the intrinsic color of the surface layer.
If you look
at (not through) your camera or binocular lens you will see a blue or reddish color - that is NOT a pigment, but an optical interference color produced in the same way colors are on case-hardened guns.
The visible colors are the net effect of refractive index of the layer (causing different retardation at different wavelengths), the reflectivity of the substrate and the light once again bouncing outward thru the layers.
It's an unusual concept - case colors are not at all like the pigment colors of paint - they are the result of the physical properties of light and interference.
