Whipping Up Booms lists the ways to make a bomb. Reading it allows the party to craft 
Oil of Combustion.
This book is redolent with the enticing smell of paper and ink.
Properties
Rarity: Common
Weight: 0.5 kg / 1 lb
Price: 14 gp
Where to find
- On a table on the third floor of Felogyr's Fireworks X: 5 Y: -129
Text
[A well-worn book of recipes for explosives, this tome's pages are stuck together with gum, sulphur paste, and ingredients you can't quite identify.]
OIL OF COMBUSTION
FROM the heart of a magma mephit (or two or three) you can craft a powerful oil that, when applies to your weapons, will set your foe alight with the force of your passion for explosive-craft! In a fray most memorable, I once used a well-timed application of Oil of Combustion to light my young son's birthday candle - and to keep the local bully tom cat at bay from the cake.