View source for Thread:RedboneBits/@comment-6030132-20130413052910/@comment-678630-20130413170553

The tier of an item is one above the highest tier of the two items used in the recipe.

For example, a Rubber Ducky is made with the tier 6 Bathtub and tier 5 Dink Duck painting. The Bathtub is the higher tier of the two, so the tier of the ducky is one above that, tier 7. If both ingredients happen to be the same tier, it's just one above the shared tier.

Hope that helps!