I did blackwork embroidery on a caul. Cauls were essentially a period hairnet. It covered the hair on the back of the female head and was usually made of fabric.
How to make an Elizabethan caul can be found on Mistress Drea's webpage at http://www.elizabethancostume.net/headwear/caulmake.html
Here is part of Bostocke's sampler from 1598, which I am basing my pattern off of.
Here is the beginning of my caul
Here is the first completed part of my caul:
The embroidery completed.
The caul sitting on a doll's head.
Examples of cauls in history:
Domenico Ghirlandaio's Portrait of a Lady (1480)
http://katerina.purplefiles.net/DOCO/Cauls_diary.htm
http://h-costume.mail.indra.narkive.com/A3hjxYC0/primary-source-for-elizabethan-pillbox-hats-sought:i.13.12.full