MinisterKohobi has done a great job importing some 4e alchemy recipies here, but when I'm DM-ing I'd rather have some general guidelines rather than so many specifics. The spell lists already give us a ton of effects, so why not piggyback off them? In order to prevent alchemy from displacing spellcasting we'll introduce a few restrictions and requirements.
Basic alchemy guidelines:
- By default, an alchemy product can recreate any spell effect and uses the same target, concentration, duration, range, and level scaling.
- By default, an alchemy product requires 1 action to use and can be used once.
- Alchemy products require no verbal components. The product itself is the material component. Applying the product (e.g., drinking, throwing, etc.) is the somatic component. Basically, alchemy products can be used like "S, M" spells.
- The level of an alchemy product is the same as the source spell (and can be "up cast" similarly).
- The time and difficulty required to create an alchemy product depends on the level of the spell effect being mimicked.
- Creating an alchemy product requires alchemist's supplies, a recipe for the product (at a given effect level), and materials for the product.
- Alchemist supplies and recipes are not consumed, but materials are consumed whether or not the creation of the product is successful.
- The materials and recipes required for an alchemy product should be gathered via adventuring and/or skill checks. Just like the market for magical items is very limited, so is the market for alchemy components.
- Alchemy products are unstable and degrade over time. They retain full efficacy for one week after creation, and half-strength for another week. After two weeks the product is inert.
Alchemy process:
- Obtain recipe (likely via adventuring or research)
- Obtain materials (likely via adventuring or purchase)
- Use alchemy supplies to create product
Base DC for recipe research, material gathering, and creation of an alchemy product. It is referred to as "Base DC" in later paragraphs. Natural 20s do not count as successes for any alchemy check.
- 10 + (product level * 2)
Process for researching a recipe that is not found via adventuring:
- Each research attempt requires x-squared downtime days, where x is the product level. (E.g., a 7th level product requires 49 days of research before a check is made.)
- As per PHB page 187, "For each day of research, you must spend 1 gp to cover your expenses. This cost is in addition to your normal lifestyle expenses."
- The check is usually Intelligence (Investigation), but could be Intelligence (Nature) or Intelligence (Arcana) depending on the circumstances.
- When the check is successful the alchemist obtains a recipe for the product desired.
Research modifiers. Add these modifiers to your research roll if allowed by your DM.
- +1 for favorable research resources (E.g., library in major city; scraps of recipe, fey garden)
- +1 if alchemist has observed the alchemy product in use
- +1 if alchemist can cast the spell that the product is mimicking
- +1 if working from an existing recipe for the same effect at any lower level, or +2 if existing recipe is for the level immediately below
- +1/+2/+3 if alchemist works in suitable permanent lab (1,000 gp for +1 lab, 10,000 gp for +2 lab, 100,000 gp for +3 lab)
Process for obtaining materials that are not found via adventuring:
- Each gather attempt requires 1 downtime day per product level. (E.g., a 5th level product requires 5 days of gathering before a check is made.)
- Gathering has no default cost beyond lifestyle expenses.
- The check made depends on the method used to gather materials (see below).
- When the check is successful the alchemist obtains the materials required for one creation attempt.
Gathering materials via purchase:
- Requires continuous presence in settlement (village/town/city) for duration of gathering attempt.
- Added cost above default: 10 gp per day, paid whether gathering check is successful or not.
- Check is Charisma (Investigation)
- Modifiers: -2 in village, +2 in city, -5 for subsequent attempts in same settlement for x days, where x is the product level
Gathering materials from nature:
- Requires movement/searching in a suitable environment for the duration of gathering attempt. ("Suitable" is up to the DM; locating a suitable environment may require a check of its own.)
- No added cost above default.
- Check is Intelligence (Nature)
- Modifiers: -5 default, +1 for each 5 miles away from a settlement, up to +5 net (E.g., +5 bonus applies when 50+ miles from nearest settlement)
Process for creating an alchemy product once you have the recipe and materials:
- Each creation attempt requires 1 downtime day per product level.
- Each creation attempt consumes the materials, whether successful or not. Recipes are not consumed.
- Creation has no default cost beyond lifestyle expenses.
- Check is Intelligence (Alchemy Supplies)
Creation modifiers:
- +1/+2/+3 if alchemist works in suitable permanent lab (1,000 gp for +1 lab, 10,000 gp for +2 lab, 100,000 gp for +3 lab)
- Roll with advantage if another alchemist is assisting. The alchemist with the lowest skill makes the roll with advantage.
Product modifiers. Apply these modifiers to the creation DC. They do not require separate recipes.
- Increased stability, +5 DC. Product stays fresh for two weeks, then retains half-strength for two weeks.
- Decreased stability, -5 DC. Product stays fresh for one day, then retains half-strength for one day.
- Double batch, +3 DC. Consumes two sets of materials and creates two identical products when successful.
- Prototype, -5 DC. Use time is the greater of 10 minutes or the casting time of the mimicked spell, instead of 1 action. Product requires Intelligence (Alchemy Supplies) check at DC 10 + product level to activate; failed check results in wasted product.
Example:
Our Alchemist is Hermes, a level 5 wizard (proficiency bonus +3), intelligence of 18 (mod +4), charisma of 10 (mod +0), and proficiency with Alchemy Supplies, Investigation, and Nature. Hermes wants to create a flashbang that mimics a level 3 fireball spell, which he knows how to cast. The Base DC is 16 (10 + 6 for a third-level spell effect).
First, Hermes decides to reseach a recipe for his flashbang. Each research attempt takes 9 days (3 squared) and costs 1 gp per day in addition to his lifestyle expenses. For modifiers, Hermes is in a major city with a library (+1), can cast the spell he is attempting to mimic (+1), and has invested 1000 gp in his permanent alchemy lab (+1). His total situational modifier is +3. Because he is proficient in investigation and has an int of 18, he also gets +7. His total modifier is +10 for a DC 16 Intelligence (Investigation) check. After 9 downtime days of researching, Hermes passes the check and successfully creates a recipe for his flashbang.
Second, Hermes needs to gather the resources for his blashbang via purchase. Each gather attempt requires 3 downtime days and costs 30 gold above his lifestyle expenses. The DC remains at 16. The situational modifiers is +2 for being in a large city. For the Charisma (Investigation) check Hermes also adds his Charisma modifier and his proficiency bonus, for a total of +5 against a DC of 16. This check is harder and requires two attempts before Hermes succeeds and gathers the materials. The two attempts take 6 downtime days and cost Hermes 60 gold.
Third, Hermes creates the flashbang. The creation attempt requires 3 days of downtime activity, and the Base DC is 16 for a Intelligence (Alchemy Supplies) check. Hermes decides to improve his chances of success by making a product with reduced stability, which reduces the DC by 5 to 11. Hermes receives a +1 due to his alchemy lab, +3 proficiency bonus, and +4 intelligence bonus, for a total modifier of +8. Hermes easily succeeds at the DC 11 check and creates the flashbang, consuming his materials. The flashbang retains full strength for 1 day and half strength for 1 day. Better blow something up quick!
I like how you've thought out your overall system, but for a "spell-in-a-bottle" approach you might want to readjust costs and time to manufacture to be less than that required for scrolls (which last much longer). One problem I have with the whole "bomb" flask idea (potions that are not imbibed) is that it is extremely dangerous to explore or carouse with these things on your person. It would be much more practical (for the potential user of one of these spell-bombs) to have a catalyzer that activates the concoction, at which time the "shelf-life" (and danger) begins.
As a DM, I could use a slight variation of your system as a means of manufacturing specific spell inks for scrolls (with the appropriate cost adjustment), as it seems ideal for such an endeavor. 
However, I prefer a more traditional sort of alchemy (based on historical hermetic systems) that basically has very little to do with the spells which D&D has to offer.
-DS
Thanks for reading 
I didn't intend to create such a wall-of-text when I started writing.
Anyway, yes, I agree that a more traditional alchemy system could be interesting. This is more of a mental experiment to see if I can piggyback on the existing "powers" in the spell system.
DarkSphinx wrote:
This looks like a good system. I will be letting my players have access to it. If they use it, I'll post some feedback for you.
I will probably limit the things they can make though, more akin to the 4e stuff like MinisterKohobi has in the 4e conversion thread, but with various 5e spells that can't be found in potion form thrown in.
Cool, let me know!
Whir wrote: