To see the thread used for these doilies, go to this site, http://www.kunststrik.dk/
and click on "Bo's Garn" in the right column. (Garn= yarn) Then click on "English translation" to read about it. It's not cotton but mulberry silk! Gorgeous!
It's fascinating to me that these round doilies were placed under kerosene lamps to spread and intensify the light.