521.
The augmentation on the minus side is less frequent; but we observe that the more pure and condensed the Prussian-blue or cobalt glass is prepared, the more readily it assumes a reddish hue and inclines to the violet.
522.
The French have a happy expression for the less perceptible tendency of yellow and blue towards red: they say the colour has "un œil de rouge," which we might perhaps express by a reddish glance (einen röthlichen blick).
XXXIX.
CULMINATION
523.
This is the consequence of still progressing augmentation. Red, in which neither yellow nor blue is to be detected, here constitutes the acme.
524.
If we wish to select a striking example of a culmination on the plus side, we again find it in the coloured steel, which attains the bright red acme, and can be arrested at this point.
525.