Supplemental resistances are not immediately obvious, but will be automatically learned by a character when they take a hit and observe their armor reducing that damage type more than normal. For example, when I'm fresh off the farm and examine my iron helmet, it's going to give me the standard resistance ratings, but no supplemental resistances. But if I get hit in the head with a nether attack while wearing that helmet ...
Note that last line about learning my helmet grants 50% supplemental nether resistance due to being made of iron. Now knowing that iron provides that resistance, any time I EXAMINE a piece of armor made of iron, I'll see that noted:An inky black phantom hurls a small inky-black glob at you!
A small inky-black glob surges toward you! Ranged(d600):192 vs Dodge(d103(1x)):9 = 183 (30%)
8 nether damage (37%) (head, helmet)
** You have learned that being made of iron, your helmet grants 50% supplemental nether resistance! **
Note that last bit saying I've observed that being made of iron, it grants 50% nether resistance.exam helm
You carefully examine an iron helmet ,..
You see nothing particularly unusual about the iron helmet.
It is a medium-sized item, mainly made of iron.
It can be worn in the helmet inventory slot.
It is a protective garment of the leather type, classified as light armor, and would afford the following levels of protection: ((ignore that it's made of iron but classified as light leather - yay for testing items))
You have observed that being made of iron, it grants the following supplemental resistance:
There are only a few supplemental resistance materials out there right now, but I think this will be a pretty fun and interesting way for players to discover them, and I'm really itching to add some more of them. Of course, player characters are free to share their knowledge ICly with one another. No reason to be all secretive about it.