Green facecloths coloured with GJM-503 and RBBR (at a weight ration of 1:1) dipped at their edges into a basic (pH > 9.0) washing solution, causing the colour to change from green to red. Left: image of an entirely new facecloth and on the right side for comparison the facecloth washed 14 times at 40° and 16 times at 60° C within a period of four months. (For interpretation of the references to color in this text, the reader is referred to the web version of the article.)