Each item that can be essentially distilled (or macerated) requires a specific temperature to produce essence. This is achieved by the mix of spirits added to the alcohol lamp. The quantity of essence produced is determined both the nearness to the correct temperature and the lowest quality of the spirits used. Using only fire spirits will return 6 essence, and it varies by 1 for each quality level, from 9 using Ra spirits to 3 using any grey spirits. Certain materials require grey spirits for maceration and thus the yield of essence has a permanent maximum of 3.
For the best known set of spirits for each type of material that can be macerated, please check the essence tables.
Telanoc's Current Working Theory About the Relationship between spirits and essences