After thinking for a while, i decided to add my own Tin ingot.
Now, i even got the recipe working, it was a fault in my code, not the ingots not being registered.
My new problem is, that the recipe doesn't output my freshly added item, wich is a combination of tin and iron, called hardened tin.
Even tough i create a new itemstack for it, it keeps on outputting the Forestry Fertilizer, but with exactly the amount i told it!
My new added items also don't show up in NEI or creative mode inventory.
What is the problem here?