In the core series games
In Pokémon Ruby, Sapphire, and Emerald, ash is collected by walking through ash-covered tall grass. The grass will have a gray appearance if there is still ash on it, and after the player walks through it, it will turn green. The amount of ash collected is counted by the number of steps the player has walked through ash-covered grass.
In Pokémon Omega Ruby and Alpha Sapphire, ash is collected by walking through piles of volcanic ash. All ash piles provide random amounts of ash, in either a small amount (approximately 5 to 15 grams) or a large amount (approximately 30 to 60 grams). The visual and sound effects produced when scattering piles of ash differs slightly depending on whether they provide a small or large amount of ash. Roughly 1 in 5 piles provide a large amount of ash.
Any furniture the player purchases will be sent directly to the PC and can be used to decorate a Secret Base. Ash can be collected on Route 113 and Jagged PassRSE, where it settles from Mt. Chimney. In order to collect ash, the player must first obtain the Soot Sack.
In the manga
In the Pokémon Adventures manga
In Tanks, but No Tanks, Anorith & Lileep, during Ruby's pursuit of being Wallace's disciple, Ruby grabbed a set of Soot Sacks from Wallace's car and subsequently ran around to collect volcanic ash. Wallace later took the material and traded it in for a flute.
In other languages