One of the critical areas which has been untouched by the purity updates so far is flame. It is present in fireplaces, stoves and torches, and is used by ovens, kilns, smelters, and smokehouses. It is one of the four Aristotelian elements, and yet has no place in alchemy? This is clearly an oversight.
The purity of flame should be based on the materials used to create it (branches, tinder, etc.) but should also carry some innate alchemy with it based on it's history. The tinder drill or flint&steel used to start a fire will give it some basic purity, and this will be averaged with the purity of the fuel, and further influenced (but to a lesser degree) by the container the flame is in (use high purity dross for your fireplace for best results).
The uses of element-rich flames will be manifold. Flame touches upon so many different aspects of the game that it will rival our beloved Humus, allowing for the enhancement of purity in places where we never had it before.
Food baked in an Oven will be modified by the purity of the Flame; Mercury-rich fire being a great boon for mushroom pies.
Pots baked in a kiln can be further modified and enhanced in the purity of your choice.
Smelters can be lit with flame that complements your Ore, to give an even more potent product.
Stoves will prepare meals with an extra bonus.
There will be a virtuous cycle in enhancing the purity of both flame and tree, as the branches of a tree are used to make the fire that sinters the pots for the next generation of tree.
A large village could specialize in all 4 types of flame, keeping multiple stoves lit with only the best fuels, using the pure torches to transfer the flame, and enhance all of their projects in exactly the way that they wish.
I feel that the addition of a new ephemeral substance whose purity may also be enhanced will add great depth and complexity to the game. I look forwards to further ideas and enhancements to the concept of Flame Purity, since the Flame topic is so broad, and believe that if we work together we can make this thread the best Flame thread that we can.