Purity

Purity affects items in dramatic ways, multiplying their effect on study, eating, and such. Living in a high purity zone (or on a "HQ node" as it is sometimes called) will therefore make everything vastly easier as you will be studying with fewer items and filling your humors with less time foraging. This multiplier is very apparent at higher levels of study and gluttony.

Purity is predicted to be a strong incentive for both trade and warfare. As high purity zones are found and fortified they will become more and more scarce, and their desirability for those more inclined to battle will grow.

Purity mechanics

<mightyagrippa> so, what's the salem analog to sqrt(quality/10)?
<loftar> It's basically the sum of the square of the individual elements (as represented from 0.0 to 1.0).
<loftar> But linearly normalized to the range 0.0-1.0 rather than 0.25-1.0.
<mightyagrippa> so, after you have the quality number in (0,1), how does it translate to humor/skill gain multiplication?
<loftar> Usually, but not necessarily, by using it to generate a multiplier from 1-10.

To calculate the raw purity, a number between 0 and 1, use [(Salt^2 + Merc^2 + Sulp^2 + Lead^2)-.25]*(4/3).

To calculate the purity multiplier for humors and skills, use (Salt^2 + Merc^2 + Sulp^2 + Lead^2)*12-2.

For example, a waxing mushroom with 20% salt, 50% mercury, 15% sulphur, and 15% lead would have

[(.2^2+.5^2+.15^2+.15^2)-.25]*(4/3) = .1133 raw purity

(.2^2+.5^2+.15^2+.15^2)*12-2 = 2.02 purity multiplier