An Arcane Transmutator is a machine added by Thaumic Tinkerer. For the price of essence, it can double nearly any item. You have to pay 4 times the essence price of the item, working well with Buildcraft and Forestry machines.
This allows you to create really huge auras. It is also a good source for getting Purus.
"After researching further into the intricacies of Aura itself, you have found out a way to directly siphon its vis, and using aspects from nearby aspectual sources, conjure it into matter. This block can accept an item to be used as a pattern to create a new one. Only simple items, in terms of aspect count, can be created, and the quadruple of each aspect from that item."
Research available after Basic Aura Manipulation.