I've found pictures of this type of sleeve that people have been making a léine with:
Since my sleeves are much too long for my arms, I think the pleats will work great.
I do feel a bit badly about making a garment without clear documentation. I'd hate to perpetuate a long line of unfounded conjectures.
I think I'm going to go through with this, and my next wool purchase will be for a Shinrone Gown. The Shinrone gown is an extant wool gown found in an Irish bog near Shinrone, Co. Tipperary, in the 19th century. It has been dated to the latter part of the 16th century. It is currently held in Dublin at the National Museum of Ireland.
So, my dear readers, have you any evidence that validates the pleating of léine sleeves? Would it be too much of an evil to wear this conjectured garment?
