for the legendary recipie you have to have the sussur bark in the inventory.
click on the fireplace and/or the bellows until it lights up.
click on the gear icon appearing on the fireplace.
click on the "+" sign in the UI, it brings up your inventory.
Drag and drop the bark to the "+" sign
Hit create or mix (can't remember what it said)
the fireplace will turn blue
close the interface and click on the gear icon again
click on the "+" sign, brings up inventory again
move a basic, normal unupgraded dagger/greatsword etc onto the "+" sign
mix/create again
forged item is in your inventory

the dagger silences an enemy, can't remember what the other types did