Again, what I'm saying is in terms of the toughness and brittleness versus metallic bending tendency, it's probably comparable to LEGO-style plastic. Which also does not bend much, and if it does, doesn't bend like what we normally think of with metal (like an aluminum can for example).
I'm not saying purified protodermis would be literally plastic, but it clearly seems to have some traits that seem more like plastic than normal metals.
It would still have metallic traits as well. You could probably best call it metal in summary, but it's also possible (being the purified state of a highly complex molecules, rather than some atomic element like iron, which is an important point since plastics are also molecules, not atoms, as far as I recall) that it wouldn't be exactly like any normal-matter material but would share traits of many. Keep in mind it's the purified state of something that in its other forms can imitate the physics of metals, rocks, water, ice, wood, and flesh. So there's every reason to think that state could be "something in between all of them" (though clearly not organic).
Clarifying because it seems that point did not get across to some of you in my previous post. I'm not saying "plastic versus metal", I'm saying metal that has some traits more in common with plastic than normal-matter metals. Make sense?
As far as why a crack would mess up the power, my theory is that the molecule's design (whether my cyberclay theory is literally true or not) is such that when a batch of purified protodermis is melted, then solidified, that heat realigned all the molecules with each other so they form an internet-style connection between each molecule. So these connections are not only holding it physically together but actually act like wires between the parts of a computer, and the processing for the power is generated along those connections.
So, if you crack it bad enough, you break too many of these connections. Without heat to tell it to realign the connections in a different way (like how our brains will do this to work around some brain injuries), it's stuck like a computer with key wires detached and cannot process the power.
This also fits with the less pure molecules having less power; less connections. Perhaps due to some extra molecules or atoms being connected to external "ports", to cause the generation of matter-imitation physics presumably, similar to recent discoveries about epigenetic "methyl group" molecules that will bind to DNA, often for the whole span of a person's life, switching off those parts of DNA, and some may even stick around on the DNA of descendants. So there'd be less processing power internally, and likely less ports for the power to actually be generated from the surface of the mask.
And it fits with the three Legendary powers not working in the same way, because IMO all three Legendary powers are programmed into all protodermis molecules (since they're "basic functions" by definition) and in the cases of those masks I think there's simply a switch turned on to make those powers run constantly (or perhaps a basic protection part of the molecule has been irreversibly removed). I think that when you forge a Legendary Mask, constant power operation runs along all the connection lines between molecules, and normally not along the extra ports on the surface.
Cracking a connection in that kind of mask would thus make active power generation point out of exposed ports, causing a "leak" effect. And Vakama's welding trick would re-fuse those connections, sealing the "leak". (They would also have no blocked ports at all, being of the highest purity, so could generate the most powerful effects from the surface when mentally commanded to do so.)
This, again, works regardless of whether my cyberclay theory about the design of the molecule is true. (The programming could be stored physically in moving parts of the molecule, or only electronically as data within charged or uncharged parts of the molecule. Lately I'm leaning towards something that uses both, because our own cells use both physical design and electric charge to function.)
i like you're idea how on great and noble masks the power flows through the outside of the mask similar to how if lighnting strikes it will follow along the surface,
where as legendary masks are so powerfull the energy is contained throughout the whole entirety of it
so if there is a scratch deep enough or a crack on any noble or great it will disrupt the flow