I don’t know of any medieval way of starching but when I’m weaving I use linen seed glue to make the linen tread hard and strong.
This is how I do it.
1. Put 2 dl linen seeds in a pot.
2. Pour over 5 dl water.
3. Boil for 2-3 minutes.
4. Take it of the heat and let it sink for 20 minutes.
5. When cold brush it on the fabric/ treads.
6. Wait until it’s dry, and heart.
The glue washes out with water. Keep glue for max 4 days, in fridge, with lid on. After that time- throw away.
I’ll tell you more about the results after Medeltidsveckan/ the Medieval week is over.
Ps. In Visby? Don’t be a a stranger😉
pps. My living room overflow is a mess, I know..