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Saturday, April 5, 2014

What is behind temperature in C41 process?

For many years my hobby has been B&W photography and I used brand chemicals to develop my films and prints. I never supposed it possible to develop color at home, even professional photographers were sending the films to more sofisticated laboratories to process clients requests.

For more or less one year, or more, I started developing C41 films. OK, first I baught a kit from Tetenal and studied what each thing does. The great handicap for many of us, by processing C41 is that the developer should be mantained at 38,5ºC, continuos agitation and last 3' 15''. This is only possible with a automatic film processor.

But many purists follow exactly those steps in order to achieve the best of their photos. I am not a purist and very distracted, I could give 16'' instead of 15'', eheheheh!

By chance I discovered Dignan's 2-bath developer, which is safe against idiots and distracted people, don't need temperature and don't need exact timing. I have read that article several times and one detail called my attention shortly: original Dignan's 2-bath developer used as second bath Potassium Carbonate whose pH is greater than that of Sodium Carbonate.

But in the Tetenal kit one of the bottles contained just Sodium Carbonate.

Dignan's 2-bath is OK, gives some color shift but in some cases makes the picture look very artistic. But as photographs that intend to reproduce exactly the objects, it is not advisable.

So, when I developed one of my last color films, I decided to use Sodium Carbonate but at more or less the recommended temperature, about 40ºC. But I measured the temperature and the pH of the bath. Aha! The solution of Sodium Carbonate had a pH of 12,6 when at 20 ºC the pH is said to be 11,6.

Then I came to the supposition that the temperature was needed to rise the pH of the bath. To be sure of that, I prepared a 1% solution of sodium Hydroxide with pH at 13,4 cold and used it as the second bath. The result is that the pictures came with much more color saturation.

Full color

I had to dessaturate them to achieve a more acceptable color picture:

Full color

Next time I will prepare a buffer solution with pH = 12,8 to be used at room temperature and hope to get the right degree of color saturation.

1 comment:

K said...

Aha, you're "Cronocrator" :-)