The amount of time you leave the plate in the acid depends on the acid’s strength (mesured using an acetometer) the room temperature and the depth you wish to give the stroke. The etching is then ready and only the finishing touches need to be applied. A retouching ground can be applied to the plate which may then be retouched as required following the lines of the previous etching. ? Liquid siccative ground. A liquid retouching ground to cover the image locally. It is applied cold using a paint brush.?