[h-cost] question about black line thread

Can anyone please explain the process that might be happening here? This is mentioned about linen thread being processed into cloth in medieval Egypt. On receiving the threads, the weaver had first to use a pumice stone to clear off their blackish crust ... One person has suggested that

Re: [h-cost] OT Padley Martyrs (was What would my ancestor have worn?)

Thank you, Kate! Gotta save up on those airmiles; I have some digging to do! Michelle ___ h-costume mailing list h-costume@mail.indra.com http://mail.indra.com/mailman/listinfo/h-costume

Re: [h-cost] [HNW] question about black line thread

On receiving the threads, the weaver had first to use a pumice stone to clear off their blackish crust ... where was this mentioned btw? Context is as much as I gave you. The author, Anna Contadini, in her Fatimid Art at the Victoria and Albert Museum (1998), is talking about the