Abstract: Means for measuring and correctively changing the thickness of a film of water on the plate of an offset printing press which includes a light source forming a spot of light on the plate with light pick-up means including a photocell producing an output signal in response to remitted light. A disc carrying two filters in symmetrically spaced sectors is interposed in the path of the light reaching the photocell. The first filter is a band pass filter which passes a wavelength slightly separated from a maximum light absorption band of water. The second filter passes a wavelength which is well separated from the maximum light absorption band of water and which lies in a region of where there is minimum change of absorption as a function of film thickness. As a result the photocell is subjected to an alternating series of "measuring" light pulses and "reference" light pulses through the respective filters.

Abstract: An inking system for applying ink to a printing plate which includes a fountain roller and a series of ink feed rollers with at least one vibrated roller or drum. Means are provided for automatically regulating the temperature of the fountain roller thereby to maintain constant the amount of ink fed over a long press run for maintenance of a predetermined full tone density. Means are also provided for automatically regulating the temperature of the vibrated roller thereby to maintain constant the printing contrast in the half tone portions of the plate. The temperature regulating means includes both a source of heat and a source of cold, making it possible to either warm or cool the rollers thereby permitting automatic operation over a wide range of conditions including a wide variation in the ambient temperature. In the preferred embodiment the temperature of the rollers is maintained by circulating a fluid such as water through the rollers from a reservoir of fluid at a controlled rate and temperature.