Consider first the two general types of colour process: negative/positive and reversal. In the former, using the most popular process C41 or an equivalent, this consists of a first development as usual followed by a rinse then a bleach/fix (and a final wash). A reversal process (which gives positive transparencies) such as E6 or an equivalent has at least one extra step - after the first development, there is a bleach stage to remove the initial silver image, perhaps followed by a clearing bath, then a second development during which the colour image is produced. With C41, the colour image is produced by reaction between the oxidised by-products of reducing the latent silver image and colour couplers which generate the actual dye image. This takes place during the first development, and the resulting silver image together with unaffected silver halides in the emulsion are removed during the bleach/fix stage. Apart from the colour component, this is essentially the same as the analogous black and white processes which many of you will have done many times. With colour reversal, the dye image is formed during the second development by a similar kind of reaction.
The critical point about colour processing lies mainly in practical procedures, primarily in temperature control; indeed this is really the only point on which it is essential to have rigorous control. Black and white development has a fair bit of latitude whilst still giving useful results. This isn't at all true of colour work, most particularly with reversal processes where there is little or no margin for error and every effort must be made to keep temperatures very close to their nominal value. These comments apply quite generally, quite apart from the film size, whether 35mm, sub-mini or large format, and if you can get it right for one, you can do it for any of them. So when I started to consider colour work, it was clear that this was the first point to be addressed, i.e. how to keep the developer temperature constant at a required level - the first development stage is always the most critical. Most colour development processes have a nominal temperature of 38° C, though other temperatures can be used with variation of development time, even if the results will be less than optimal. My initial trials used a large tank of water heated to a couple of degrees above that actually required. All solutions and the tank were preheated and placed in it to equilibrate. Over the relatively short development time (3¼ minutes nominally) there was little change of temperature and quite satisfactory results were obtained without much difficulty. The main difficulty lay in getting a large mass of water to the right temperature, and in this I had a piece of luck. A science laboratory in a local college had disposed of an unserviceable water bath containing a thermostatic control and circulating pump, the latter having siezed and they didn't have time (or money) to fix it. This I was able to do myself without too much difficulty and the effort paid off handsomely. This device enabled me to keep all components in a water bath at any desired temperature for a long as necessary.
The set up looks something like this:
The rectangular black object is the tank itself. On the right of it is the temperature controller
whilst on the left is a frame which supports the tank and two bottles in the water which is kept at 38°.
Bottles fit into the smaller holes whilst the tank fits into the larger hole and is kept in place with a large glass paperweight !
The only other two items which are essential are an accurate thermometer and a reliable clock - digital timers are OK but personally I prefer a clockwork driven device with a large, luminous and easily read dial.
Readers may well say that I've an unfair advantage with equipment like this ! Perhaps true, but similar equipment could be made from the devices available from aquarium supplies where heaters, thermostats and circulating pumps are all available. With some ingenuity and experiment, an equivalent device should be quite readily constructed. But maybe this will give you some ideas ?
Another point that needs to be mentioned is to do with preparing and storing the solutions themselves. Whilst it is possible to prepare one's solutions completely from first principles, this does require access to a supply of the reagents themselves, some of which are quite toxic and need careful handling, and may not be at all easy to get hold of. On the other hand, complete colour processing kits of various sizes for both C41 and E6 are quite readily available from most good photographic suppliers. For example, in the UK, a proprietry C41 kit can be purchased on the High Street for about £14. Using the developing system I've described on other pages, this will provide enough solution to process about 16 sub-mini films i.e. less than £1 each or about 3p (~ ¢4) per frame). If one has a good quality negative/transparency scanner, colour images are possible at very low cost with all the advantages that digital manipulation can bring.
Going back to the reagents themselves, it's particularly important to be aware that the solutions, developers in particular, are particularly prone to degradation by oxidation through exposure to air. If one will be developing a good number of films from a batch of stock solutions over an extended period, then it's essential to have a method of storage which excludes air as far as possible. There are many methods for this - you could use collapsible bottles, though these are hard to find small enough; you could fill the bottle up with marbles !
My solution is a little unorthodox but it works. From my local camping shop I obtained a plastic, roll-up water carrier of about 1 litre capacity. These usually have some kind of snap seal to prevent leakage. I removed this and attached a wide piece of plastic tubing in its place, into which was fitted a tap. In use, the developer is transferred from its bottle into the water container, the tap assembly fitted firmly, and after squeezing to expel air, the tap is shut. This keeps the solution out of contact with the air. To dispense the required volume, the whole assembly is inverted and suspended from a beam over the workbench. On opening the tap carefully, the required volume can easily be dispensed. My set-up uses a glass tap with a teflon core derived from a broken analytical burette, but other taps could easily be used, though from my own experience, plastic ones should be avoided if possible as they tend to stick after a period of use. Maybe this should give you some ideas:
I mentioned that some experiment will be necessary for best results. In my case, I found that if I used the nominal conditions for first development: stock diluted 1 + 2 and develop for 3¼ minutes at 38° C, the result gave rather dense negatives which are very hard to scan, with the scanner working toward the limits of its sensitivity and giving quite a lot of undesirable artefacts. After some experiment, I found that much better negatives resulted with a dilution of 1 + 3 and a reduction of development time to 2¾ minutes. Film scanners generally, I've found, work better with negatives a little on the thin side compared to what might be used for conventional work. So if you first results aren't all they might be, don't hesitate to try different conditions.
I hope this gives you some encouragement to give colour processing a try. It really isn't as hard as many would make out and you may well be surprised by the quality of the results.
A little PS, courtesy of Ilford. It's normal practice to thoroughly wash films at the end of processing, but with colour stock where this is done at 38°C this can be awkward. Ilford propose the following: after rinsing the tank following the final fixing stage, nearly fill it with water (at the right temperature), fit the cover and invert five times. Empty the tank, refill again and repeat ten times; finally repeat twenty times. You can safely increase the number of times if you wish. This uses a lot less washing water, and provided you don't use a hardening fix, will very adequately clear the emulsion of all soluble reagents, certainly for all practical purposes. I found that a film so washed passed the permanganate test for thiosulphate perfectly, so I wash all my films this way now. So far I haven't had any problems whatsoever and it saves a lot of water and time. Give it a try.
Last updated February 2003