Kodak manufactured their own filters in the plant in Rochester. The Wratten trade mark is a Kodak property and the filters were dyes coated with a gelatin coating machine. The supports were on glass or 'plastic' film support. They were made in two grades, one for use sandwiched with negatives and one for use between the lens and the paper in the case of printing. IIRC, they were also made in the plant at Harrow outside of London.