This study aims to improve the photometric calibration of astronomical photo plates. The Sonneberg Observatory’s sky patrol was selected, comprising about 300,000 plates, and the digitization workflow is implemented using PyPlate. The challenge is to remove zero point offsets resulting from differences in color sensitivity in the photo plates’ emulsion response. By utilizing the Gaia DR3 dataset and the GaiaXPy tool, we are able to obtain a consistent astrometric and photometric calibration of the Sonneberg plates and those of other archives such as APPLAUSE.