RE: [pure-silver] Re: PIQUED MY CURIOSITY; was Phenidone in alcohol ----- Original Message ----- From: mail1
To: pure-silver@xxxxxxxxxxxxx Sent: Friday, May 08, 2009 2:13 PMSubject: [pure-silver] Re: PIQUED MY CURIOSITY; was Phenidone in alcohol
I also would keep an eye on PH. With D-76 there has been some mention of an increase in negative contrast as PH rises.
Kodalk DevelopersDK-40 the fist in a series of Kodalk developers from Kodak was for motion picture positive film D-42 is a normal contrast developer for photomicrography. D-42 is missing the K because it is formulated with Borax and Kodalk DK-50 is a developer for roll films, professional films and plates. DK-50r replenisher DK-60a is Kodak's Kodalk deep tank or machine developer for Kodak roll films
DK-60b is Kodak's Kodalk aero film developer.Aha, now that you mention DK-60b it rings a bell. I may even have the formula for it somewhere.
The rising pH problem seems to be specific to D-76 and similar developers. It is caused by a reaction betweeb the hydroquinone and sulfite. This produces a small amount of sodium hydroxide which causes a slow rise in pH. In the paper on D-76 the rise in pH is such as to about halve the required developing time to reach a given gamma over a period of a month. This is assuming the developer is not used. Kodak's answer was to buffer the developer by using equal amounts of borax and boric acid. The developer activity can be varied over quite a large range by changing the proportions of the two. This was of value where it was desired to control contrast without changing developing time. Kodak also published a Kodalk version of D-76 sometimes labeled DK-76. This is identical to normal D-76 but contains 2 grams/liter of Kodalk in place of the Borax. Originally, Kodak thought the Kodalk would have sufficient buffering action to prevent the pH rise but turns out to be less effective than the buffering. Developers like DK-50 and DK-60A are more alkaline than D-76 and don't seem to suffer from the rise in pH. One advantage of using borax or Kodalk as the alkali is that it does not effervesc in acid solution eliminating any problem from bubble formation in the stop bath or fixing bath. Kodak published Kodalk versions of a lot of different developers after its invention of a cheap method of manufacturing the stuff. There was never a paper developer for some reason but the proprietary developer Ektonol is a Kodalk containing paper developer. I don't have even a guess at the formula for Ektonol although I have its MSDS somewhere.
-- Richard Knoppow Los Angeles, CA, USAdickburk@xxxxxxxxxxxxx
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