DUSTING OR GRAINING IN PROCESS WORK (Fr., Grainage ; Ger., Staub hornung) There are several processes of photo-engraving dependent on the laying of a ground consisting of fine resin, bitumen, or other similar material. Such a method is used for aquatint etching instead of the old way of flowing on the resin emulsified in alcohol.
For a process of colour work much practised in France, called chromo-typogravure, a resin grain is laid on zinc plates, and a set-off is laid down on the plates from a key plate to guide the etcher in stopping out the various colours. This is done by means of an acid-resisting varnish, so that the resin ground forms the lighter tints.
In the photogravure process the laying of the ground is an important operation. Finely powdered bitumen is generally used, and after being deposited on the copper plate and fixed by heat, a carbon print is developed upon it to form the resist for etching.
The dusting for the foregoing processes is done by means of a dusting box. This may be of either the turnover pattern or the fan pattern, the former being suitable for small plates and mostly used by amateurs. The box is turned over and over to shake up the bitumen, then the plate is put in and the box allowed to stand for a shorter or longer time, as may be demanded by the character of the grain required. In the fan dusting box the powder is stirred up in the semicircular zinc bottom by means of a revolving brush, and, after allowing to stand for a few moments for the heavier particles to settle, the plate is put in. The longer it remains in the box the finer will be the grain. Powdered lac is also sometimes used for dusting.