Item repair

Item Repair is a feature added in Beta 1.9 Pre-release 3 and allows players to repair damaged Tools or Items by combining them on a Crafting grid. Items can be placed anywhere on the crafting grid. The two weapons/tools the player is repairing must be of the same type and material for it to work. The health of the item that is repaired depends on the amount of health left in the two used items.The resulting item will have slightly more uses left than the two original items. Therefore, repairing is slightly more useful than just space conservation as what might be initially deduced.

Even if an enchanted item is used in repair, the result will not be enchanted.

Algorithm
The general algorithm is currently only known by testing, but such tests on pickaxes revealed completely linear behavior: the uses of the resulting item is the sum of previous uses (with the max durability cap), plus a number depending on the material: 2 for gold, 6 for wood, 12 for stone, 24 for iron, and 155 on diamond, being completely independent of the initial uses distribution (one almost new and other one almost broken, both half-broken, etc.). Tests with other tools show the same results.

Facts
tools made of different materials cannot be combined e.g wood pick and a stone pick