Simon Manchester has been known to err. Here is a sentence from an encyclopedia article
"After pulling down the goods to a soft, silky condition by bating or puering, it is
necessary, after scudding, to plump them up again and bring them into a clean and fit
condition for receiving the tan."

There is logic to "puer", no logic to "pure". If figures that clerks knowing Latin used "puer"
and clerks who did not copied the sound as "pure".

Here is URL to encyclopedia article. It is very long, and you have to scroll down halfway to find
the quote given above.
http://28.1911encyclopedia.org/L/LE/LEATHER.htm