- Paper treated with turmeric: used to indicate the presence of alkalis, which turn it brown, or of boricacid, which turns it reddish-brown.
- It is used to detect boric acid and borates.
- The paper is dipped into the sample containing hydrochloric acid (pH 1-2). Afterwards it is allowed to dry. In presence of borate the paper turns orange to red. In the absence of borate, sodium hydroxide leads to a brown-red color.
Yellow paper dipped in an acid solution (such as vinegar) does not change colour appreciably. The same paper dipped in an alkaline (basic) solution (such as sodium carbonate, soda ash or washing soda) turns a deep red colour.