Ektachrome film has three separate light-sensitive layers; each layer is sensitive to a different group of wavelengths corresponding to red, green, and blue colors. When the film is exposed, each layer records a latent image based on its sensitivity. A yellow filter prevents blue light from exposing the green- and red-sensitive layers, which have some sensitivity to blue light. Films are processed at with a tolerance of only ±0.5°F; exceeding these limits could cause color shifts. The steps are: The original Ektachrome process introduced in 1946 used similar steps with different durations; the total processing time was approximately 90 minutes. It was renamed to E-1 when the E-2 process was introduced in 1955 for ASA 32 Ektachrome, followed by E-3 for ASA 50 Ektachrome in 1959. Films designed for E-2 and E-3 are prone to fading because of the instability of the color dyes. The processes were phased out in 1974 in favor of
E-4 (which was introduced in 1966), and two years later
E-6 was introduced which remains in use to this day. ==References==