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Decorating Defects - their cause and cure

Black Japan greening when Varnished

Black japan is a useful material,
but one which occasionally gives trouble to the decorator.
It is a rich black varnish, the most important constituent of which is black asphaltum.
The complaint most frequently made against it is that although it may appear a dense black when it is applied, it occasionally assumes a greenish hue when varnished.
This defect is due to the fact that the varnish has been put on before the japan is absolutely dry.
It may be observed that it is extremely difficult to know how soon it is ready to be varnished, and the fact that, when touched, it gives no sign of tackiness does not necessarily imply that it is dry all through.
Greening frequently takes place when the japan has been put on in too thick a coat.
It is essential that plenty of drying time should be allowed between coats, and also before varnishing, if this defect is to be avoided.
If greening does take place, the best treatment is to apply another coat of the japan and to revarnish.