Colour Printing

This tutorial aims to give you the ability to make high quality colour prints using the Kaiser VCP enlarger and the Durst Printo unit. Most of the tutorial is about the intricasies of exposing the print – the Printo system is just the preferred method of processing.

1. First prepare the chemicals and pocessor

There should be some ready mixed colour processing chemicals in large brown concertina bottles below the chemical shelves. If there aren’t, you’ll need to mix some up according to the manufacturers instructions. It’s best to mix up as much as will fit in the large bottles, as some chemicals inevitably get lost when emptying the processor. There are some heavy duty rubber gloves in the darkroom – wear these at all times when handling or mixing colour chemicals, as they are very dangerous.

Once you have the chemicals ready, you’ll need to dismantle the Durst Printo, rinse the rollers and make sure they move, as shown in the pictures below. Do not turn on the unit until you have put in the chemicals – it will rapidly overheat and become damaged.

Once the rollers are clean and moving freely, reassemble the unit apart from the lids on the chemical wells. Pour the developer very carefully into the section labelled ‘developer’ (this should be the section closest to the intake rollers – if it’s not, take apart the processor and reassemble it so that the wells are in the right order), making sure you spread the chemical the whole length of the rollers. Now put the lid on this section and pour the bleach-fix (or ‘blix’) into the other chemical well, again being sure to coat the rollers thoroughly. Put the lid on. You can now plug the unit in, make sure the temperature is set to 25 degrees and turn it on.

Setting up the processor may take a long time, but until the end of the session, you don’t have to worry about it – it keeps the chemicals at the right temperature and you can simply feed your unprocessed paper in at one end, turn on the lights and two minutes later your print rolls out. Now all you’ve got to worry about is getting the print right.

2. Put the negative in the enlarger

Clean the negative and the glass in the carrier, checking for dust with the lupe and light box. If you are printing from 35mm, you may wish to replace the non-Newton glass with a 35mm mask to prevent light fogging from the edges of the negative. The masks are kept in the paper drawer, and are put in as shown in the pictures below.

3. Compose and focus your picture on the easel

This step is identical to the same step in black and white printing.

4. Make a test strip

As you cannot use any lights at all for colour paper (the Maxilux safelight claims to have a setting that is safe for colour, but even that will fog if it is kept close enough to be useful) the accurate method is impossible.

To make a colour test strip, set the enlarger filters to 70 yellow, 70 magenta and 0 cyan while the lights are on, then turn off all the lights and make sure there are no light leaks anywhere. Remember to cover up any LED’s, such as the ones on the paper dryer and the enlarger timer.

In complete darkness, cut a wide (4cm or more) strip of paper, preferably along the length of the paper you are using. Expose this as for the lazy method in black and white printing, but with a fixed interval exposure of 4s and no ‘base’ exposure – on a strip you will probably be able to fit exposures of 4, 8, 12 and possibly 16 seconds. The smaller number of exposure sections occurs because you cannot see the paper while the enlarger is off, so you have to move the mask by guesswork.

Still with the lights off, find the intake slot of the processor and lift the flap. Allow the rollers to gently take in the strip, narrow side going in first. When you can, put the flap down over the end of the strip yet to be taken in – you can now turn on the lights.

Sit and twiddle your thumbs until the test strip emerges from the other end of the unit. Pick it up with tongs, and rinse it thoroughly in the wash tank. Squeegee the water off, and inspect. The test strip should have a good range of densities, from too light to too dark – choose the exposure that best suits your picture (one is usually looking for a good range of detail with dense blacks and clean whites, but it’s often difficult to find these in an area localised enough for a test strip). This may be between two test exposures – just average them out. The exposure will change anyway as you change the filtration.

5. Test pieces

Now you have to find the correct filtration to get the colours in your picture right – this is the hard bit, but it gets easier with practise. Before you start, make sure the filters are engaged, with the lever on the side of the enlarger.

Examine your test strip. Are there any very evident colour casts in the correctly exposed section? Everyone has different ways of doing this, but a good way to start is to find a tone that should be neutral – say a neutral black or grey. Let us assume that you notice the blacks look rather magenta. To correct this, you would add some magenta filtration – say you start with 70 magenta, you would now increase it to 80 magenta. Next, take another strip of your paper and expose it with the new filtration and the test strip exposure (plus a small amount to compensate for the reduction in light reaching the paper – see filter factors later). Process as before, wash and inspect:

Are the blacks still magenta? If so, add some more filtration (5 points for a subtle cast, 10 points for a medium and 20 points or more for a heavy or very heavy cast) and print another test strip.

Are the blacks neutral? Now you can make a final print on a full sheet of paper.

Have the blacks gone green? In that case, you added too much magenta – decrease the magenta fitration by 5 points and make another test strip.

It will feel rather counterintuitive at first – if you want to remove a cast of a certain colour, add filtration off that colour. The amount of filtration you have to add or remove is something that becomes much easier with more practise, as does identifying the colour of the cast in the first place. Things that can help with these problems are viewing filters (there is a set of these in the darkroom – treat them carefully, they are delicate) that you hold over your print to test different filtrations. Alternatively, you could make a ‘ring-around’ print – these contain examples of different colour casts at different strengths, so you can directly compare your test print to them. A ring-around is shown below – be warned, this does not show the exact colours of the potential casts, as this will depend on your monitor and/or printer.

Ring-around

The central print is correctly filtered, the next ring out has a 10 point cast, the next a 20 point cast and so on. This will also give you a good idea of the actual colours of the cast, though bear in mind that you will often have more than one cast on a print. If this is the case, just treat each cast separately: if you have a print with a cast that looks orange, this will be a mixture of yellow and red. To correct this you need to add yellow filtration and red filtration, which is equivalent to adding equal quanitities of magenta and yellow. To clarify – if you had a cast that was 10pts of red and 20pts of yellow, altogether you would add 30 yellow and 10 magenta.

To avoid confusion when calculating filtration, we usually leave the cyan filter alone and use only the yellow and magenta. Only use the cyan filter if you have such a strong cast that you cannot avoid it – for instance, if you’ve already taken out all the magenta and yellow, but the print still looks cyan.

Colour of cast How to correct
Green Subtract magenta
Blue Subtract yellow
Magenta Add magenta
Red Add yellow and magenta
Yellow Add yellow
Cyan Subtract yellow and magenta

I mentioned earlier that exposure times change according to how much filtration there is. The table below allows you to calculate the revised exposure times – if you add the filter, multiply by the filter factor: if you subtract a filter, divide by the filter factor. For example, if you had an initial exposure of 10s and you added 20 magenta, you would end up with an exposure of 15s.

Filter factors
Filter strength yellow magenta cyan
5 1.1 1.2 1.1
10 1.1 1.3 1.2
20 1.1 1.5 1.3
30 1.1 1.7 1.4
40 1.1 1.9 1.5
50 1.1 2.1 1.6

6. The final print

Right – all casts corrected? Exposure correct? Take a full sheet of paper and make a full print. After seeing the whole thing, you may still want to make the odd tweak, but you’ve done most of the hard work Congratulations!

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