My magus wants to make "missing component" potions. The idea is that they would allow the creation of "grenades" that only work on specific creatures or in very specific situations. Please kindly put away any assumptions about the Medieval Paradigm while reading this post. If you've read any Dresden Files you should be fine.
The original idea, pretty specific to our unusual Saga, is a substance we can coat our grogs' ammunition in that is completely inert in day to day situations. The coating is specifically designed to inflict extra damage on Red Court Vampires. Originally I'd conceived this as an extra +5 Ignem damage but, on further consideration, I feel the best way for the potion to "recognize" Red Vamps is to be made with Vis harvested from them, which is Perdo. So a Pe Co potion effect for +5 damage or so.
A second similar idea would be to make a Pe Te potion effect (again, coating ammunition) that causes a bullet to explode like a torpedo when submerged in ocean water (or in brackish water in general, making it usable in estuaries).
Just how far out there is such an idea, in your opinion, WRT to how the rules on Hermetic magic and labs work?
My magus has an Affinity with Terram; might I be better off enchanting batches of slugs and shots using a variant on the potion rules instead of using actual potions?
The term potion refers to any salve, incense, paste, powder, ointment, or similar substance you wish to make; though potions are often in liquid form, they don’t have to be.
Potions in AM4 generate their effect on what they are used on. They can be nearly any form, including the bullet of a round of ammunition. So you do not require a "variant" of the potion rules.
Since you are designing an effect, then having it only activate under certain situations would just need to be included in the design. You could do that by ether including some sensory requisite in the effect or designing an effect that works on the specific target.
For example if you want to make something blow up on contact with salt water, you could design a potion effect that causes salt water to explode. Something like a ReAq effect that turns saltwater instantly to steam could be very nasty.
I believe this is the first time I have ever marked a topic as Solved. Much thanks, @InfinityzeN, not only for your input but also for remembering we still use 4th ed.
I have asked him probably half a dozen times if he used 4th edition in older threads. Many of his older questions suggested it and I wanted to be sure. It has been often enough that I remembered this time.