Chapter 4
Brushing-up LiquidI will describe each detail of the brushing-up liquid which involved in the primary materials except plywood:
The brushing-up liquid is used for making sensitivity higher for fat and acid. The prescriptions vary according to the materials of each printing plate.
Metal plate starts being oxidized from grinding the surface of the plate, so it needs using the brushing-up liquid for returning the printing plate to first condition before first drawing. The brushing-up liquid fixes the sensitivity and removes dust of grinding.
Also it needs using the brushing-up liquid for redrawing after made printing plate: the printing plate is returned to first condition by the brushing-up liquid.
4.1. Limestone Printing Plate
Acetic acid (glacial acetic acid) [CH3COOH] is used for the brushing-up liquid. Mix 10-20 parts glacial acetic acid to 100 part water.
First, powder with the rosin and the talcum powder on the ink in condition leaving the ink on the part of image: these powders and the ink protect the part of image from the brushing-up liquid.
Apply the brushing-up liquid onto necessary part or the whole on the surface of the limestone with brush after wetting the surface of the limestone by washing with water or wiping down with a damp sponge on the limestone.
Leave the situation as it is for 5 minutes and let the brushing-up liquid react on the limestone. Wash the surface of the limestone clean with water and dry the limestone, and re-draw.
4.2. Metal (Aluminum/Zinc) Printing Plate
Chrome alum saturated solution [chromium(III) potassium sulfate 12-water / KCr(SO4)2·12H2O] and or add 1-3% nitric acid of chrome alum saturated solution is used for the brushing-up liquid.
Apply the brushing-up liquid on the surface of the metal plate with brush before drawing image for making the film of aluminum sulfate [Al2(SO4)3·16H2O] and zinc sulfate [ZnSO4], respectively: it makes the sensitivity higher for fat and acid.
Leave the situation as it is for 1-5 minutes and let the brushing-up liquid react on the metal plate. Wash the surface of the metal plate clean with water and dry the metal plate.
For re-draw, first of all, powder with the rosin and the talcum powder on the ink in condition leaving the ink on the part of image: these powders and the ink protect the part of image from the brushing-up liquid.
After powder, apply the brushing-up liquid onto necessary part or the whole on the surface of the metal plate with brush, and re-draw.
4.3. Polyester/Frosted Glass Printing Plate
Just only wash the printing plate well with neutral detergent for the polyester or frosted glass plate.