Hard to say what that is in the pictures - it actually looks somewhat like a fungus/mould. Could also be some sort of mineral deposit, perhaps the copper has reacted with something and formed a coating made of some copper compound. Scrape a little bit off and stuck it under a microscope... See if it is soluble in water, do a pH test if it is. If not - see if it's soluble in acetone/isopropyl alcohol. See if a small amount burns under a flame - if so - what colour does it burn?
Not sure about the chameleon cloaking stuff ... Although I will point out, it is possible for a beam to disappear midair and then reappear further on if there are no particulates in that patch of air for whatever reason... Although usually you'd need some sort of container to isolate that patch of air so that it doesn't mix with the surrounding environment.
Can you post larger pictures? What happens if you try to scratch it?
Looks like rust at a glance, but I have no idea.
" this doesn't look like any of the Iron Oxides I'm familiar with - nor does it look like Copper Oxide"
Yeah. That's why my first thought was mercury----amalgamated copper. The flame test color for mercury would be red if I remember correctly so copper amalgam should be sorta yellowish green, but not the bright yellow of sodium.
English yes, history I actually enjoyed, just went way way way ahead of the class, which earned me an annoying nickname, that fortunately did not stick.