Vis is the main concept from Thaumcraft Vis is the mystical energy that is the main component brought to Minecraft. Vis is found in solid form by most items. You can tell how much vis is contained in an item by looking at its Vis Value. Vis is also found in the atmosphere, called the Aura.
Vis and TaintEdit
Vis comes in two forms: Pure vis and Taint. When burning an item in a Crucible, half of the Vis value is converted into Vis and the other half into Taint. Taint is not usable for most thaumaturgic devices unless certain Discoveries have been found.
Goggles of Revealing are a wearable tool that can allow you to see the local Aura--namely the Vis and Taint levels in a chunk. If the Vis count becomes too low, or the Taint becomes too high, the chunk will become Tainted.
How to Get VisEdit
There are two types of devices that put Vis into a usable form. The standard device is the Crucible. The Crucible will burn items in exchange for half of their vis value. More advanced Crucibles will improve the net yield of vis, like the Crucible of Eyes and the Thaumium Crucible. The other half goes to Taint. A better way to get Vis, however, is the Vis Condenser. This device draws pure Vis from the Aura. Monitor the aura closely if you do this though. Low levels of vis may trigger a Taint infestation.