Medieval faire dating
It belongs to a garment often referred to as St Elizabeth's Cloak.Very early examples of single-needle knitting known as nahlbindning are found throughout Europe during the pre-medieval period.
It seems unlikely to me to wash out afterwards, and I don't know why, if ink is one of the ingrediants, it was not just used watered down by itself.
In 1304, two women wool merchants, Aleyse Darcy and Thomasin Guydichon, are recorded as having sold to the Earl of Lincoln:for the huge sum of 300 marks.
It doesn't record what the cloths intended use was, but it does give us an idea of the possible size of cloth manufacture at that time.
It was found in a London deposit dated before or around 1500.
There are a few other examples of two-needle knitting from early England- gloves, vests and caps.