The Softened Diamond Mass is a tricky piece of business. It is crafting by smelting a Softened Diamond in any sort of furnace. The problem is once it is in your inventory you have 7 seconds to use it before it turns back into a diamond.
The Softened Diamond Mass has a life of 7 seconds. This countdown does not start until the Softened Diamond Mass is in the players inventory. Once the 7 seconds count down the Softened Diamond Mass is removed from the player and they are given back their diamond.
Place 1 Softened Diamond in any sort of furnace.