The Infusion Altar is a multi-block structure that can be used to make a variety of advanced items through the process of Infusion. Its creation and use represents a thaumaturge's graduation into advanced magical crafting.
Most of the Altar is made of Arcane Stone in various forms: The original blocks, bricks of the same stuff, and in the middle, a pedestal. . This will be crowned by the Runic Matrix, which is a separate crafting requiring an Ender Pearl. Naturally, all of these parts can be crafted on the Arcane Workbench. To activate the Altar, right-click it with a wand, upon which it should abandon the confines of blockiness, and bend into a curved structure, with the Matrix itself rotating defiantly upon one corner.
While the Altar is fairly complex in its own right, it does not stand alone: For actual use, you will need to add additional pedestals and stabilizer items, and also provide supplies of essentia, not to mention the material ingredients for your recipes. Note that if any block of the structure is mined, the altar will be broken: part or all of the structure will revert to its original shape, and it will not work until the block is replaced and the altar is re-activated with a wand.
Note: Arcane pedestals are made in pairs, and those surrounding the altar are also used in pairs. The central pedestal of the structure will therefore leave you with one odd pedestal... just keep that in a chest somewhere until you're ready to use it for a Recharging Pedestal. While pedestals can be used for mere display of items, it is important not to do this within 9 blocks of the Altar, or you will interfere with the infusion process.