Learned something fascinating from the Återskapat #podcast. Amica Sundström and Maria Neijman have activated a major #Medieval source material that nobody seems to have touched before. There is no mention of it in the bibliographical databases. The huge KLNM encyclopedia has a single sentence about it: "Seals were often protected by fabric or leather bags and, towards the end of the Middle Ages, by metal cases" (15:194).
The National Archives in Stockholm hold hundreds of these seal bags. They're made from Medieval fabric that has been kept indoors, in the dark, since they were made. They pretty much retain their original colours! It's a fabric sample archive! With calendar dates!