When any acid is applied to the writing on this paper the blue stain of Prussian blue appears.
Its presence was only to be detected by the blue stain it gave off during its growth.
Only occasionally did I catch the blue stain in the eyes of the throng about me.
From the plant indigoferae was obtained a blue stain, known as indigo.
The face and body were painted with red and white ochre and a blue stain.
The young trapper had, in effect, hit the mark in the very centre, as the blue stain of the bullet testified.