LITMUS

Kind of basic test (that turns red or blue) (6)

Solution has appeared in 3 crosswords (0 across and 3 down):

• Quick crossword No 16,617 — 2023-08-08 23:00:40
  16D: Dye material from lichens, used in acidity tests (6)
• Quick crossword No 16,278 — 2022-07-08 23:00:49
  4D: Colouring material used in acidic/base testing (6)
• Quick crossword No 15,974 — 2021-07-18 23:00:42
  5D: Kind of basic test (that turns red or blue) (6)