Achorion mould
From Discworld MUD Wiki
Achorion mould one of the ingredients used to create Achorion Purple poison.
Where is it Found?
The largest source of mould is in Ohulan Cutash.
How is it Aquired?
Mould can be scraped off of walls using a knife or dagger, in the room that it is growing. You will require some skill in crafts.husbandry.plant.herbal to be able to spot and scrape the mould.