Resensitizing solution is used to adjust the sensitivity of lithographic plates to grease.
The process differs for metal plates and stone plates. The surface of metal plates begins to oxidize as soon as it is roughened and therefore the solution is used on the plate before printing to restore the surface to its original texture and remove any residue shavings from grinding. It is also used when retouching after the plate has been made to restore the surface sensitivity to the condition prior to making the plate. The resensitizing solution is made by adding 1 to 3 parts of nitric acid to 100 parts of a saturated chrome alum solution. Coat the solution onto the entire plate with a brush, leave for about 5 minutes to react, rinse with water and allow to dry. If even a small amount of the solution remains on the plate, there will be too great a reaction and the plate will be unusable so it should be rinsed thoroughly. When retouching, this process should also be carried out after coating the ink-packed plate surface with resin powder and talcum powder.
With stone plates, the solution is used during retouching after making the plate. The solution is made by mixing 10 to 20 parts of glacial acetic acid to 100 parts of water. The plate containing the platemaking ink is first coated with resin powder and talcum powder, wiped over with a wet sponge, and the solution is applied to the damp areas to be retouched with a brush. Leave to react for 3 to 5 minutes, rinse off and allow to dry before retouching.