alchemist's fire

Alchemist's fire is a flammable liquid that can combust in a large explosion with even a tiny spark. Without a spark to ignite it, alchemist's fire is not dangerous, though you shouldn't drink it. It is roughly as healthy as drinking modern gasoline.
Alchemist's fire will burn scarlet red for about two minutes (or four cinematic combat rounds). During this time, the flames burn green and will not be doused by water or smothering. If alchemist fire combusts in water, the water will not cool the flames but it will drastically suppress the radius of the explosion.
After this time, the flames turn orange and behave as ordinary fire from then on, continuing to burn wood and other flammable substances. If the target was a person, the flames will probably peter out entirely which may or may not be a relief to the indivdual assuming they are alive.
Unlit alchemist's fire can last for decades if it's sealed in an airtight container. Alchemist's fire exposed to open air starts loses potency after four weeks in a dry area or two weeks in an area with humid air and becomes useless glop after sixteen weeks or eight weeks if exposed to dry or humid air respectively.

Using alchemist's Fire in RPG mechanics

20 d10s from Wikimedia Commons

Most of the time, I prefer narrative dice-less descriptions, if the story requires an alchemist fire to consume 100 soldiers, or two ships, or one castle tower then it will destroy 100 soldiers, two ships, or one castle tower.
But if the PCs are directly involved, it is probably not fair or desierable to have the villain's alchemists fire auto-kill the PCs or have the PC's alchemist's fire auto-kill the main villain.
We are going to call about a half cup a "potion vial". Usually, weaponized alchemist fire is kept in glass orbs with either one or two potion vials worth.
One vial of alchemist fire will hit about a one foot radius, inflicting three dice of damage the first round, then two dice, than one, than zero.
Two vials of alchemists fire will hit about a two foot radius, inflicting four dice of damage the first round, then two dice, then zero.
4 vials worth will hit about a four foot radius inflict five dice of damage the first round, then three dice, than two dice, then zero.
8 vials worth will hit about a seven foot radius, inflict six dice of damage the first round, then four dice, then three dice, then two dice.
16 vials will hit about a fifteen foot radius inflict seven dice of damage, then five dice, then four dice, then three.
32 vials will hit about a 30 foot radius, inflict eight dice of damage, then six dice, then five dice, then four.
The above is the maximum dice of damage, past this point, adding more alchemist's fire will hit more targets with a bigger fire, but it will not create a hotter fire.
Regular armor, worn, natural, or magically generated works, but soaks are at +2 difficulty. Even energy specific magic boosts from divine Protection or the Abjuration Spell, energy shield soak damage at +2 difficulty. Making protection against alchemist's fire unreliable though magical effects that lower armor soak difficulty work normally.
The damage dice assume the target is hit hit square on by burning alchemist's fire. If the target is merely grazed by the alchemists fire, reduce the damage dice accordingly.

Creating Alchemist Fire in RPG mechanics

Creating alchemist's fire is a simple Dexterity + Alchemy extended roll, difficulty 7 in a full stocked lab, +1 difficulty if working in an improvised lab, +1 difficulty if working with budget or improvised materials.
Every three successes on the extended roll will produce a vial's worth of alchemist fire. A failure will waste a lot of materials, roll Wits + Alchemy to try to minimize the loss. A botch while making alchemist fire will mean the alchemist either injures himself, burns down a large portion of their lab, or both.
The base material cost is about 20 silver pieces per vial, or 12 silver pieces per vial if working on a budget. Typically, alchemist's fire has a 30% markup when sold commercially.
Top notch glass vials cost about 2 silver pieces each, easily throwable orbs cost about 4 silver pieces each, and double-vial throwable orbs cost about 10 silver pieces. At larger quantities than this, glass containers are rarely used.
You don't need to be an alchemist to make glass containers, you need a glass blowing focus of the regular Crafts skill. For long term storage, alchemist fire is typically kept in very thick ceramic containers, usually buried underground far from any inhabited area.
Lightable fuses only cost about a silver piece or two, which can be folded into the cost of a throwable orb. This style of throwing orb with a fuse was developed by the famous historical alchemist, Moltov.

Throwing an orb of alchemist fire

Note that it is quite possible to accidentally knock off or extinguish the fuse while throwing a lit orb of alchemist fire.
If you roll one success to hit a target, that is a "marginal success", so in most cases you only grazed your target with alchemist fire liquid and it failed to ignite.
If you hit a target with two successes, they are probably doused with the liquid but the liquid did not ignite or maybe it did ignite but the target was only grazed (flip a coin to determine which outcome).
Three successes means you hit your target square on and the alchemist's fire ignited. Five successes means you probably grazed a secondary target in addition to dousing your main target.
Botches with alchemist fire are always memorable.

Can an alchemist specialize in alchemist's fire?

Yes, many do. Alchemist's fire is in high demand and it is disastrous to get wrong. Many customers refuse to deal with alchemists who do not have a proven record for producing alchemist's fire safely.
On the other hand, many alchemists refuse to deal in alchemists fire. Many alchemists have pacifist leanings, others simple are risk averse and don't want to die in their own lab.
In other words, a majority of alchemists either manufacture lots of alchemist's fire or they don't make it at all. Even if alchemists refuse to deal in it, they probably know how to do it. The recipe for alchemist fire is relatively simple compared to other alchemist mixtures. Making alchemist's fire is delicate, but it is not complicated.

Parent Technologies

• alchemy

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