Every nova has a Base Taint of 1. For every 10 Taint points gained, the Base Taint automatically increases by 1. Increasing Base Taint does not "spend" accumulated Taint points, and Base Taint does not decrease when the GM spends Taint. In effect, a characters Base Taint measures how much Taint the character has ever had. 

• The height of social rolls involving baseline characters must equal or beat the nova's Base Taint rating.
• You can choose to gain a number of Taint points equal to your Base Taint every round (see below).

Base Taint does not increase above 10.

Any time that you need to spend Quantum, you can choose to gain a point of Taint instead. Additionally, if at any time you're at zero Quantum you may gain a point of Taint to ignore the negative effects of this condition for the rest of the round. In a single round you may not gain more Taint points than your Base Taint rating.

The GM can "spend" accumulated Taint as though it is experience points to buy new miracles, add nasty Extras to your miracles, add new Flaws to your miracles (this would cost the same as adding the equivalent Extra), pay for new Intrinsics (Monstrous), and so on. This is always done for the purposes of making a character less human... buying a couple of Hard Dice in Interrogation or Persuasion, for example.

Novas that gain a lot of Taint are obviously going to become more powerful, which is in keeping with the setting, but as the GM is making all of the decisions about how to spend it you should find that a) players are wary of gaining too much, and b) additional powers bought don't make the Tainted Nova unbalanced compared to the rest of the PCs, because the GM should be keeping an eye on balance.

A character might start the game with some Taint points - gaining +1 character creation point during character creation for each point of Taint that he accepts, up to a max of 10 (which would automatically raise his Base Taint rating to 2).