turmeric paper

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Paper saturated with turmeric and used to detect the presence of alkalis, which turn the paper brown, or boric acid, which turns it red-brown.

GNU Webster's 1913

1. adj. (Chem.) paper impregnated with turmeric and used as a test for alkaline substances, by which it is changed from yellow to brown.