Color developer agent history

Color developers evolved pretty much in the sequence CD-1, CD-2, CD-4 and CD-3.
CD-1 is Diethyl-p-phenylene diamine, CD-2 is Diethyl-3-methyl, p-phenylene diamine, CD-3 is N-Ethyl, N-Methane sulfonamido ethyl-3-methyl, p-phenylene diamine and CD-4 is N-Ethyl, N-Hydroxy ethyl-3-methyl, p-phenylene diamine. They are available only as salts of HCl, H2SO4 or p-Toluene Sulfonic Acid. In kits they are prepared as adducts of SO2 gas in a rather exotic preservative solution.

CD-1 is very non-polar and has low water solubility. It goes bad fast and forms a black tar in developers on keeping. It causes some degree of dermatitis on contact with skin. The dyes formed are “flat” dyes that are “planar” and have rather low dye stability.

CD-2 is the same compound basically, but with a 3 methyl group that forces the dyes to twist out of planarity. This causes a rather large shift in dye hue so different couplers have to be used for proper color. It also causes a big improvement in dye stability due to the non-linear nature of the dyes.

The above dyes are very non-polar.

CD-3 is of medium polarity and low in activity. It is very low in causing contact dermatitis, but due to its large molecule, the dye portion is protected after formation and the dye is very stable. In most cases it requires benzyl alcohol or high pH to form a good, active develper unless a good set of couplers is found.

CD-4 is the most polar, and active of these developers. Due to the fact that it is so “hot” it will react rapidly with almost any coupler to for a dye, but the dye hues are very shifted due to polarity. Also, due to polarity, the dyes, unless specifically tailored to the developer, are far less stable. Therefore, it took many years to fully commercialize this developing agent with a good set of dyes.

Ok then, cross over a coupler set from any one of these to another of these developing agents and you see that the dye hues shift, become broader or narrower and have different dye stabilty! This is what you get from cross processing or just taking the motion picture couplers and stick them into the Ektar film.

The C-41 developer is very much like a B&W developer. Nothing is really special here. The image quality is generated by the emulsions and the couplers. Special DIR (Developer Inhibitor Release) couplers are used to tweak image sharpness and correct color and colored couplers or Masking Couplers are used to adjust the color. These differ in MP films due to the need for making internegatives and for SFX in motion picture.

In reversal processing, the first developer is very foggy and creates all of the edge effects for sharpness. It is basically a slow, weak developer that is very high in acutance. It does allow for some color correction as well due to the diffusion of development products between layers. For this reason, it does not use HQ. If it did, the effects between layers would be off by quite a bit, so image structure suffers if HQ is used. It develops 100% of the silver. I’ll explain that later.

The fogging step totally fogs what was not developed in the first developer, therefore if any silver halide were left in areas that were to be totally clear, there would be dye because the color developer is designed to go to completion.

The E6 color developer is a very high solvent, very foggy developer with a “colorless coupler” in it. The high solvent effect causes development to go to completion very forcefully, but the colorless competing coupler limits dmax, keeps dmin as clear as possible, and also limits the lifetime of oxidized developer helping the dye clouds remain as small as possible and also keep the image as sharp as possible. Most of the image structure comes from the first developer, but the color developer “tweaks” it.

So, this explains color developers and color developing agents. It also explains why cross processing can cause problems with dye hue, crossover and also explains why one film formulation just cannot be transported to another process. The entire film must be virtually redesigned from the ground up. Depending on the difficulty of this process it can take from 1 – 5 years for a complete dedicated team of emulsion makers, product designers, coaters and processing techs.

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Post time: Jan-15-2019
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