One of the many quests in Hollow Knight Silksong requires you to find a strange substance called Plasmium, which can be hard to locate.
The Alchemist's Assistant quest is triggered when you meet the Alchemist in Wormways, which is an area that could take a few hours for you to reach. When you meet Zylotol for the first time, he will ask you to find three Plasmium samples, spread all around Wormways.
