I keep collecting trophies items with tooltips that say on them “used in crafting”. With such a wonderful descriptions I just kept hording them all and figured I would figure out their true use some day. Well that day is here, they appear to be most often used on the mastery tab of an item in order to increase your chances of a critical success.

So with a bit of searching in the Lore Book, I made a quick list (which I will update over time) of the items I had and which professions use them:

Torn claw = weapon smith / woodworker / tailor
blackened claw = weapon smith
Delicate wing = woodworker
delicate horn = woodworker
clouded eye = scholar
Dark eye = scholar
blackened tail = metalworker
small intestine = cook
crushed intestine= cook
torn intestine = cook
Dismal treasure = jeweler
copper salts = Scholar

I also refined an advance search on the Lore Book site to list all the rare trophies from level 7 to 20. You can use that list to find an item and see what items it is used in.