DuPont Formula

11 maggio 2006  Pier-Luigi  Formule (0)
I have never seen a developer with bicarbonate except as a buffering agent. Metol will develop even in slightly acid conditions but very slowly. It works fine at neutral pH as in Kodak D-25. If it worked as you envision it would produce high contrast images where, in fact, D-23 has good shadow detail and yeilds about the same speed as D-76. The difference is developing time for the same gamma, D-23 takes longer. Adding Borax will increase the activity and decrease the developing time. An example is very old DuPont formula for motion picture negative film. This was the result in DuPont´s research into D-76 type developers. romide has an effect on film speed. As developer is used it accumulates reaction products. One of these is bromide. Bromide tends to restrain the development of fog grains but at some point will also restrain the development of halide grains with little exposure. For this reason used developer will have the effect of lowered film speed even when developement is carried out longer. Metol is relatively less sensitive to bromide than Hydroquinone. At the low pH of D-76, D-23, D-25, and the above developer, metol does not produce much fogging so bromide is not necessary. When a carbonate is used bromide becomes necessary because the higher pH causes more fog. At the pH of D-76 Hydroquinone is nearly inactive as a developing agent. Its function is regeneration of the Metol. This results in somewhat greater capacity for D-76 than for the DuPont formula or D-23. However, the slow reaction between Hydroquinone and sulfite produces a small amount of hydroxide which causes the pH to rise over a period of time. Kodak´s cure for this was to buffer the developer by using a combination of Borax and Boric acid. Current packaged D-76 is of this type. DuPont found that the addition of Hydroquinone had no practical advantage and just left it out although later DuPont developers did include it. It should be noted that highly active developers like Dektol (D-72) do not produce high film speed due to the necessity for considerable bromide. The literature is filled with research on all sorts of developers and combinations. Such publications as _The Journal of the Society of Motion Picture and Television Engineers_ and _Photographic Science and Engineering_ as well as extensive patent data will reveal all. 1. "Borax Developer Characteristics" H. W. Moyse and D. R .White (DuPont Redpath Labs), _Transactions of the Society of Motion Picture Engineers_ Vol. XIII, No. 38, 1929 p.445

 

Water (at 125F or 52C) 750.0 ml Metol 5.0 grams Sodium Sulfite, dessicated 75.0 grams Borax, granulated 5.0 grams Water to make 1.0 liter

 

postato da Patrick Gainer su rec.photo.darkroom

 

Development times are similar to D-76. Because this developer does not contain Hydroquinone its activity does not rise on storage.

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