A skill about breaking down items in a non-buyable way and using the resource to create utility items that benefit current content.
https://oldschool.runescape.wiki/w/User:Aluzim/alchemy_skill_suggestion
Old School RuneScape Wiki
Alchemy is the skill of transforming matter into other forms of matter. The central aspects of the skill are an untradeable, stackable item that is gathered through skilling gathering (you still get skilling experience) and item drops and making devices that have a wide array of benefits. Small amounts of experience gained by transforming items ...