Abstract: A method and apparatus for producing a highly readable diazo copy from a blue line original. An illumination source provides actinic energy which is substantially absorbed by the blue image of a diazo blue line print and in which no substantial exposure of the diazo paper can occur from energy which is non-responsive to the blue image. The light source produces major energy in the range of about 4600 to 5900 Angstroms. A filter or other means is provided to remove any spurious wavelengths which are non-responsive to the blue image and which can expose the diazo paper.