Demonstration of Thenards Blue

Chemicals needed

aluminum chloride, hexahydrate

cobalt(II)-chloride GSGESUND.gif (476 Byte) Xn    R 22    S 22-24/25

One can use instead of the chlorides the corresponding oxides/hydroxides. If one uses silicon dioxide instead of aluminum chloride smalt results, boric acid also yields a colorant.

Equipment needed

test tube (heat resistant)
burner (preferably gas-)

Test procedure



One can formulate the formation of Thenards Blue as follows:

2 AlCl3 + CoCl2 + 4 H2O --> CoAl2O4 + 8 HCl


DSCN0215.JPG (178075 Byte)

Formation of Thenards Blue


derived from "9. Nachweis als Thenards Blau", p. 425, [7]