Topic – C-41 and temperature control

One reason, perhaps the reason, my home colour developing never really was spot on may well have been lack of temperature control.

I have tried using a bath of tempered water for all the chemicals of the Tetenal C-41 kit but it is not that easy really. How long should the PET bottles with the chemicals be in water to get to the right temperature inside? Five minutes? Fifteen? Fifty? Either way it is not easy to keep a constant temperature of the water for prolonged time.

I usually start with 45C water, drop the bottles into that and let them be there until temp has fallen to 38 or 39C. That is when I start develop.

Recently I set upon making a more proper temp controller. From was bought a  temp controller with relay output and a solid state relay capable of switching no less that 40A of 240VAC! A small plastic housing was made and the parts installed. Next came the hunt for a heating element of some 400 – 600 watts. And that is what I have yet to find. Until then I got a 200W aquarium heater. It actually had a temp control built-in so I had a go with that just for fun.

Note: A power of 200W is way too little to be really useful. It takes ages to heat the water in the first place. Though it does keep an already tempered water at the suggested temperature all right.

tempreg (7)

The quick setup in the sink consists of the heater at the far end, the pump at the bottom and a precise thermometer for process control floating on a bit of foam.

Apparently heating aquariums is a pretty sloppy business as fish are too stupid to really care, while developing colour is a different business where exact control is said to be needed: The hysteresis of the built-in regulator was something like +/- 2C. And the scale only went up to 32 C so some slight massacring of the scalewas necessary to be able to increase its range. It seems to work even afterwards:)

A trial run was made with the aquarium heater and a 220V pump intended for making water splash around in ponds. The water was wildly circulated and everything was guaranteed to have the same temperature after a few hours. The actual temperature was supervised with a Taylor 9842 digital thermometer calibrated at 0C. It took several hours of heating before entering a steady state of 38-something C.

The procedure was a usual, 3m45s dev (due to overused developer), and 10m blix. As the blix runs to exhaustion I am no longer picky with the suggested 4 minute period. I tried to keep the Paterson tank submerged in the 38C water at all times possible. It all went very well and the colour casts I usually get were gone! I am onto something here!

IMG IMG_0008 IMG_0006 IMG_0001 IMG_0005 IMG_0004

The end result is that the setup works but I look forward to a more precise heating and control apparatus in the future. It would also be pleasing with the heater, pump and controller as a single unit instead of the present cable mess in the kitchen!

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2 Responses to Topic – C-41 and temperature control

  1. Pompe says:

    i dont use c-41 but i noticed that you are trying to keep a stable temperature in a vessel that is actually a humongous heatsink !

    instead of the kitchen zink use a plastic container insulated with “liggunderlag” that is what i use when brewing beer and over a hour a i get a drop in temperature of only a couple of degrees. so methinks holding @ 38 C for the time it takes to develop a reel of film should be no problem

    metall transfers heat. stainless steel kitchen sinks transfers heat very rapidly. surface of the water in the sink =X surface of the kitchen zink =10X so cooling surface of the water is….. you get where i am going with this right ?

    o and thanks for all of the good reading material on your blog,

  2. jabcam says:

    First of all: Thanks for commenting! It is always nice to know that someone actually reads my ramblings.

    Hmm, I never really thought there would be such large difference using a plastic container than this metal one. As the metal is rather thin I could get away with cladding the underside of the sink with the liggunderlag-foam? Perhaps the 200W heater will suffice then? Interesting! Needs more experimenting:)

    I keep all my photo stuff in two large plastic containers from Ikea. If I relieve one of these from its contents that would be a nice developer bath. Must try!


    PS Fun to know you are brewing at home. I dabble with that from kits (mostly British bitter) now and then.

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