Active Anvil

[Brenem]

Find a clickable anvil from each of the areas and hold armor in right hand with Iron bread in left, then click anvil
You can only do an anvil from each area once per armor.
You can upgrade other items like helm, boots, robes and bracers but not just any.
Only certain items can be upgraded. The Iron bread will poof and no upgrade will happen if an item can't be upgraded.
If it works, you will see two numbers in scroll. I assume the 1st is damage absorption and the 2nd is the amount that was added.

Each anvil ads 2% to A/C according to Seiyrias site.

The clickable (active) anvils move around at resets and after use all 5 charges on them. (So, recheck the anvils that you found before that were not active when a reset happens)

I know the green armor from sullen keep, boots from sullen keep, helm from sullen keep, Ozo bracers, robe from IR and the spur robes can be upgraded.
More known gear that you can add bread to are Santa gauntlets and boots.
I know the gauntlets from food guardian can't be. (it takes bread but shows 0 added)

[Brenem]

I am 99% confident that there are 45 active anvils out of 134 total.

I have teleports and twigs to every anvil. One early morning when I am nearly sure was only one in IR, I checked every anvil
and came up with those numbers.
It is possible that I may have missed one or forgot to write down an active anvil is why I say 99% instead of 100%