Alchemy is a very old science, and its techniques have improved over time. GMs may consider implementing the GURPS notion of "Tech Level" for Alchemy. Tech Level 0, Stone Age alchemy, would have invented few formulas and would originally have used laborious hand labor for its results, along with many useless techniques. It is essentially herbalism. In the modern day, human Alchemy is Tech Level 7 (and still a long way from Tech Level 8), is much more scientific (though still a deep mystery), knows many more recipes, and can efficiently use the tools of modern chemistry. Divine and Infernal Alchemy may be as far as TL9. (In a certain sense, of course, alchemy is all TL16.)
Various schools of human alchemy might be teaching at different Tech Levels; since alchemy is not a publically-dispersed academic study, there arises the possibility of pockets of great backwardness as well as the occasional isolated genius ahead of his time. In such a case, alchemists in the campaign would have access to materials which would determine their effective Tech Levels; an ancient religious tradition with a few rituals might never have passed beyond a limited TL1, while an alchemist working from a strange old Renaissance book would be working at TL4. The Society is presented at TL7.
An alchemist with Alchemy at some Tech Level would find a recipe from a higher Tech Level very difficult; vice versa, a more modern alchemist would have to puzzle through what he considers irrelevancies and flawed theories or obsolete techniques to use a recipe from a lower TL. An alchemist can increase his effective TL by studying a book's worth of new recipes and techniques; rules for increasing one's TL are up to the GM, but a month of eight-hour days of study per TL difference, followed by passing an Intelligence (in GURPS, IQ) roll, is not unreasonable. Each fail requires studying again, and each pass increases your TL by 1. Someone who does so should note on his character sheet that he can still use lower TLs of Alchemy without penalty. Alternatively, someone may choose deliberately to study, say, techniques from the Roman alchemical tomes, and eliminate his penalty for using those.
On the other hand, if an alchemical recipe is designed for use with primitive equipment, no penalty need be assessed for working without advanced equipment, assuming the alchemist knows the lower-tech version; two interesting possibilities are the Healing Potion and the First Aid Kit. Knowing the TL0 version of this alchemical recipe and talisman would allow an alchemist to use the most basic tools -- probably nothing more than fire, stone bowls, water, and careful work -- to create a working Healing Potion or Medicine tool, assuming the appropriate natural ingredients could be found. Costs would essentially be $0 if the ingredients could be found in the wild, and the alchemist would suffer no skill penalty for working under wilderness conditions.
A brief summary of the TL rules, based on the GURPS form: working with a TL 1 level higher than your own incurs a -3 penalty to In Nomine Alchemy skill or a -5 penalty to a GURPS skill; 2 levels higher, -6 or -10; 3 levels higher, -9 or -15; and you simply cannot understand something 4 TLs higher. If you are dealing with a recipe from a TL 1 lower than your own, you are at -1 to either kind of skill; 2 levels lower, a -2 to In Nomine skill or -3 to GURPS skill; 3 levels lower, a -3 to IN skill or -5 to GURPS skill; and so on at a cumulative -1 in IN or -2 in GURPS.
Recipes would become available at various TLs, and research would gradually bring most to TL7 in the Society. At the GM's discretion, some the Society knows may still be at lower Tech Levels, due either to lack of research interest, classified status, or some unknown difficulty in updating it(meaning TL7 alchemists would all be at penalties to use the recipe without additional study). Some lower-tech versions may be preserved for various reasons of utility. Different societies like the Ignes may know such recipes at modern TL, or not at all, or know some the Society does not, at any TL.
Older items would likely have had different names (a Bronze Age alchemist would not have called a recipe "Forcefield Bubble"). A small peak in research occurred during the Bronze Age but alchemy fell into slow times in the following centuries; the Renaissance saw a boom in invention followed by a gradually accelerating pace of advancement.
If the Tech Level rules are used, here is one possible timeline of alchemical invention. Items listed at Tech Level "8+" are known to exist, but their recipes are not fully known to the Society. A typical human member will not have access to those recipes, though an angelic member might.