Item Damage, how does it work?

[Terageld]

This problem has been gnawing at me for a few months now. I do not know how my items get damaged. Back in the day, Terry wore a tattoo of a red dragon on his chest. One month, the tattoo would occasionally get damaged in battle. Nothing else got damaged, not even the breastplate over the tattoo. My tattoo was damaged to the point where it fell off. I guess that's why they invented laser removal.
I'm having this problem again. This time, my aketon is getting damaged. I think it might have something to do with layer (my aketon is worn in the same layer the tattoo was). After ten minutes of fighting, my aketon was reduced from "perfect" to "bad."
I've had a few other issues with item damage before. One of them was a claw weapon that I used until it got damaged to the point that I couldn't use it anymore. I've also noticed that damage happens to items when they are covered by armor. I was occasionally take damaged on my concealed pocket (underneath my vambraces) or my hidden knife sheath (underneath full-plate greaves).
I've also never taken item damage to my armor or my swords, even though they are the ones that do most of the brutal fighting.

[Alitar]

Non-magic or non-masterwork items are much more susceptible to damage. I believe certain materials have greater or lesser chance for being damaged.

[Lirith]

You can also repair any item, either at an appropriate merchant who sells the same type of item, or by another player with a spell. There should be no reason why any item you have ends up as scrap unless you don't have it repaired when damaged.

[Terageld]

Problem is, some merchants cannot repair certain things, like tattoos, my claw weapon, or my garrote (made out of silk).
I'm not too worried of my stuff getting damaged. I'm just thinking of the realistic aspect of the game. How can my aketon get damaged when I have a coat and a breastplate over it? It seems the things that I wear "close to the body" are more able to be damaged.

[Nearraba]

Your weapon and garrote definitely are repairable (in way Lirith explained), the tattoo... not so much that I'm aware. I am honesty not certain how the Hardcode works for this and understand the concern, however one way to think of it for your realistic aspect: you're getting hit, punched, kicked, what have you and sure your over armour is taking the brute of it, but that underneath is taking damage too via moving, snagging against the other. And one to many hits to a body part, of course any tattoo is going to look bad. Given, there also is no code for when you get hit so hard, your helmet flies off, etc. Just one way to look at it, if adjusting affected layers cannot be changed.