Scumbling, the opposite process to that of glazing, is done by going lightly over the work with an opaque tint, generally produced by an admixture of white. For this purpose a hog-hair brush is employed, charged with colour but sparingly; and with it the tints are drawn very thinly, and somewhat loosely, over the previous painting, which should, as in the case of glazing, be dry and firm. Scumbling is used to modify certain effects, by rendering the portion to which it is applied cooler, greyer, and in fact less defined than it was before, and to give air and distance to objects that seemed too near. It is thus of service both in correcting a tendency to muddiness or dirtiness of colour, and to what may be called hardness or over-distinctness of detail, and in weakening the force of colours that are too powerful by softening and uniting such tints as may be too violently contrasted. It is desirable to avoid, as far as possible, scumbling over shadows, as an inexperienced hand might thus destroy their transparency.