We propose that iron sulfides can be formed in the first bowl of a commercial wool scour. Under the low redox conditions recorded, ferric iron, a ubiquitous component of minerals on the fleece, is dissolved reductively to the ferrous form, which reacts with sulfide present either as residual depilatory on slipe wool or from degraded wool protein. The black iron sulfide may deposit on the scoured wool, making it dull and gray. The observation that some scoured wools become brighter and more yellow with time is consistent with the expected behavior of deposited iron sulfides, which slowly oxidize in air.