Upvote:5
The Cairo Geniza, a repository of letters, accounts, etc. saved by the Jewish citizens of Cairo during the Middle Ages, has documentation for the use of starch on fabrics between the 10th and 13th centuries. "When a household ordered from a grocer half a pound of soap and another half of 'nasha', starch, one understands that a big wash was ahead, and that some, or most, linen was starched". S.D. Goitein, "A Mediterranean Society" vol. IV, p. 183 (UC Berkeley Press, 1983).
Upvote:6
One thing to notice about ancient clothing is its general drapiness, like today's saris in India. There isn't much place for stiffened fabrics. (Boucher's 20,000 Years of Fashion covers early costume well) In Indo-European languages territory, the fabrics were woolens (don't starch), linen (can starch but no evidence of it), and cotton in the eastern range (ditto). When linen was stiffened for Egyptian or Grecian armour, the layers were gummed, not starched.
We do know that starch was used to stiffen food, like sauces, as we still use cornstarch today. (* The Horizon Cookbook and Illustrated History of Eating and Drinking Through the Ages * which has good recipes)
That the roots for words for starch in different languages go back to Proto-Indo-European doesn't mean the PIE had starch, or even that Classical peoples starched their clothes. I believe if you check you will find the roots for computer and ordinateur go back to PIE, too. :D
The earliest I can think of starch moving from the kitchen to the wardrobe is the Middle Ages for starching veils and wimples.