When a transparent colour is laid upon another of a different nature, it produces a mixed colour, different from either of the simple ones which compose it. This is observed in the smoke coming out of a chimney, which, when passing before the black soot, appears blueish, but as it ascends against the blue of the sky, it changes its appearance into a reddish brown. So the colour lake laid on blue will turn it to a violet colour; yellow upon blue turns to green; saffron upon white becomes yellow; white scumbled upon a dark ground appears blue, and is more or less beautiful, as the white and the ground are more or less pure.