Abstract: A developing fluid for positive-acting, negative-acting and reversible lithographic printing plates comprises a metasilicate as alkali together with an ethylene oxide/propylene oxide block copolymer and, optionally, sodium tetraborate, a phosphate ester, and anti-foaming agent and a water-softening or sequestering agent. The fluid has a high alkali content for reducing the need for frequent replenishment while at the same time minimizing damage to the image particularly in negative and reversed plates and avoiding unacceptable foaming and turbidity.

Abstract: The invention relates to an automatic machine for the reversal processing of lithographic printing plates which are required to be exposed overall after heating. The method and apparatus of the invention provide that the exposure be effected while the plates are being conveyed through water in a shallow bath.