From the site http://www.photomemorabilia.co.uk/Co...rly_Kodak.html :
In September 1941, Eastman Kodak began two types of colour print services:
(i) mainly for amateur photographers taking pictures on 35mm Kodachrome film, was for “Minicolor Prints”, which were available in 3x or 5x enlargements from 35mm transparencies, and
(ii) aimed mainly at professional photographers who were, by then, using the new “Kodachrome Professional” sheet film, introduced in 1938, to make large transparencies. By 1943, this film was obtainable in sizes up to 11ins. x 14ins. This more elaborate and expensive service was for “Kotavachrome Professional” prints, obtainable from original Kodachrome sheet film transparencies. Before printing, a black and white contrast mask was made from each sheet film transparency which, when bound up with the transparency before printing onto the Kodachrome print material, had the effect of lowering the image contrast, resulting in improved highlight and shadow detail in the finished print. Kotavachrome prints ranged in size from 8ins. x 10ins to 30ins x 40ins.