This is my idea for an Alchemy/Astrology mystery based on Fuego's studies of Gerber...
Alchemical Periapts
Lesser Alchemical Periapts – Minor Mystery Virtue
Alchemical Periapts are similar to Astrological Periapts; it is mainly a cosmetic difference between the two. Alchemical Periapts come in the form of vials, powders, elixirs, potions, salves, and whatnot. Charges are represented by the number of doses/uses/applications he generates.
Alchemical Periapts use a mix of Astrology and Alchemy, using the rules on p.48 of TMRE, but modified for flavor. You create a Periapt Horoscope as normal, rolling a Stress Die + Intelligence + Artes Liberales (Astronomy), against an Ease Factor of 9+. However, the Maximum Level of the effect equals 5 x Philosophiae (Natural Philosophy). The number of resulting Charges equals your Lab Total divided by 5 (round up). This is fractionally less advantageous than Astrological Periapts, as this relies on two different scores. However, as an equal bonus to offset this, you can gain a Bonus to your Lab Total (and Maximum Effect Level) by using Special Ingredients (as per Shapes & Materials, and likewise restricted to a limit of Magic Theory).
Greater Alchemical Periapts – Major Mystery Virtue
This includes all of the effects of Lesser Alchemical Periapts, and if the Initiate already has that Virtue, then this replaces that (which counts as a Minor Ordeal for the loss of a Virtue). This Virtue requires Planetary Magic and either Vulgar or Hermetic Alchemy.
In addition to those effects, this Virtue allows you to instill Ritual Effects into Periapts. This procedure is fundamentally different, but uses a similar formula. Drawing up a horoscope does not provide a Lab Text advantage, but it is still required in order to perform this procedure. The roll is a Stress Die + Intelligence + Artes Liberales (Astronomy) + Philosophiae (Natural Philosophy), against an Ease Factor of 9 + (the magnitude of the Ritual effect). The Maximum Level of the effect equals 5 x Philosophiae (Natural Philosophy).
Your Lab Total must of course equal or exceed the effect, and you gain a potential number of charges equal to (Lab Total – Level) divided by five, rounded up. You do not to craft that many charges, choosing a lower amount (minimum of 1). Each charge requires vis equal to the magnitude of the ritual effect, and since you are limited to 2 x Magic Theory pawns per season, getting the maximum number of potential charges may be tricky. You still get your Special Ingredient bonus, which adds to your Lab Total and to the Maximum Effect level. This bonus also adds to the amount of vis you may use. If you used Philosophic Alchemy to distil vis into your ingredient materials, then you can use this vis as an additional bonus (Philosophic vis doesn’t count toward your limits).
Example: Fuego of Flambeau has a Creo Corpus Lab total of 65. He wants to create a salve that improved any one wound one level. This is a 20th level Ritual effect, so his Ease Factor is 13. He has an Intelligence of +5, Artes Liberales 4 (Astronomy), and Philosophiae 5 (Natural Philosophy). He rolls a 2, so his total is 18, and he succeeds. With his Lab Total, he has the potential for 9 charges. However, his Magic Theory is 11, which allows him to use 22 pawns of vis in a season. That’s only enough for 4 charges. Using Special Ingredients he can use up to 33 pawns, enough for 7 charges. If he can somehow squeeze three pawns of Philosophic vis from his ingredient choices, then he can gain his full potential of 9 charges. Later, he wants to make an elixir that improves all wounds by one level, a level 30 ritual effect. He has a maximum potential of 7 charges and requires 6 pawns per charge. He needs 42 pawns of vis to get his full 7 charges, at least 9 of which would have to be Philosophic vis.