Salem

Here is and idea that I came up with after today's update.
It aims to prevent the node system of H&H, where only a lucky few had control over the high quality nodes, without sacificing any of the complexity and variety that the new purities add.

Basically:
If you harvest any rescource (water, clay, herbs, wildlife, whatever), the tile it was harvested from (/killed on) loses some percent in the highest of it's purities for that rescource, and gains some in it's lowest.
Another tile, in a radius (x) around the harvested tile, gains the purity that was lost on the harvested tile's highest, and yet another tile in radius (x) loses the purity that was added to the harvested tile.
Obviously, the effect of harvesting recources in large quantities, like water and clay, should have less of an impact than collecting a herb or killing a bear.
This way, players can 'farm' a purity node over time, for whatever kind of product they want to harvest.

To go with it, I propose a new tool: the Alchemical Probe.
The Alchemical Probe can be wielded like a shovel, and activated with the dig command. It has one inventory slot. It can be used to determine the alchemical properties of a tile, without altering it's percentages like havesting would. To use it, put an item (clay, granite, lime, herb, animal cut) in it's inventory slot, equip it, and dig. This will cause to he item put into it to turn into 'goo'. This goo will have the alchemical properties that the harvestable item put into it's slot would have when harvested from this tile. Very handy for farming purity nodes.

EIther proficiences, or a socketable item could influence the percentage gain and loss on the tiles that compensate for the change on the harvested tile, to make node farming more efficient.

Thoughts?

Wouldn't this result in everything eventually approaching 0%

I don't think so.
Especially not with either proficiency levels, or a socketable item increasing the gains and loss on the target tiles slightly, compared to the gain and loss on the harvest tile.
You could ofcourse ruin it by harvesting exactly the wrong tiles in succession, but there's where the alchemical tool comes in handy, to prevent that.

Also, since most purities will start really low, there's more room to grow than to shrink. Compare going down from 25 to 0 (if you start with 0% purity) with going up from 25 to 100. When a tile compensates for gain on the harvest tile, it cannot go below zero, and any overflow will not go to any other tile. This gives a strong bias towards purity increase on average, rather than balancing out to 0% pure.