VARIABLE DENSITY OPTICAL SOUND
Western Electric Disney's Flowers & Trees. 1933 Three-strip Technicolor. Silver soundtrack.	Fox Movietone Thunderhead, Son of Flicka. 1944 Filmed on Technicolor Monopack, Technicolor dye transfer print. Silver soundtrack.

VARIABLE AREA OPTICAL SOUND
Unilateral Variable Area Unknown German film 1933 Ufacolor Dye soundtrack.	RCA Photophone Duplex Variable Area Snow White & the Seven Dwarfs 1937 Technicolor successive exposure Silver soundtrack.
Duplex Variable Area Unknown U.S.A. 1949 Cinecolor Dye soundtrack.	Dual Bilateral Variable Area The Man Who Never Was 1956 CinemaScope - Eastmancolor Silver soundtrack.

All black & white films and most color films used a silver based soundtrack. Some color processes used cyan dye based soundtracks that yielded a generally inferior sound quality in addition to being detected by the projector's sound reader as being of lower volume than a silver track. The dye based track was less costly because it was printed at the time that the picture was printed to the film. Silver tracks required several additional steps in order to create a small band of black & white film along the picture edge upon which the sound image was photographically printed. Believe it or not, dye based soundtracks are being forced upon the theatre industry once again. This time the excuse is "environmental reasons". Exactly why the soundtrack in the Cinecolor example at bottom left is green remains a mystery to the Curator.