Diazotype developing apparatus with liquid metering assembly

Apparatus for developing exposed diazotype sheet material by applying a predetermined amount of liquid developer to the sheet material, said apparatus comprising:

• a frame;
• an applicator roller mounted for rotation in a given direction upon the frame, said roller having a generally cylindrical surface;
• a metering blade mounted upon the frame and urged against the surface of the roller;
• means for supplying liquid developer at a first area of the roller surface located before the metering blade in a direction opposite to said given direction;
• means for urging the sheet material against a second area of the roller surface located beyond the metering blade in said given direction;
• a sheet having at least one surface which is relatively smooth and continuous;
• and
• means mounting the sheet upon the frame for movement between a first position, wherein the sheet is interposed between the metering blade and the surface of the roller, with said one surface of the sheet confronting the surface of the roller, and a second position, wherein the sheet is withdrawn from between the metering blade and the surface of the roller;
• the sheet being hard enough to preclude the formation of unwanted impressions upon the surface of the roller by the metering blade when the sheet is in the first position.