Appearance
RA-4 printing process
RA-4 is the standard process for making colour prints from colour negatives. Light is projected through the negative onto colour paper to form a latent image, which chemistry then develops into a finished print. Three things make it more involved than it first appears. The paper must be handled in the dark, the chemistry is temperature-sensitive, and the colour has to be balanced with filters.
Working in the dark
Colour paper is sensitive to every colour of light. Unlike most printing papers, it cannot be handled under a safelight. Load and process it in complete darkness. The alternative is a light-tight drum or print processor, which lets the room lights go back on once the paper is sealed inside. Decide where everything sits and rehearse each step by touch before the lights go out.
The chemistry
RA-4 needs only two chemical baths and a wash, all run warm at 35°C. Hold the developer to within half a degree by standing the bottles and trays in a temperature-controlled water bath. Drift here is the main cause of colour shifts.
Colour developer can make skin sensitive after repeated contact, so wear gloves. The darkroom safety guide covers handling and disposal.
| Step | Time | What it does |
|---|---|---|
| Developer | 45s to 1min | Builds the image |
| Bleach-fix (BLIX) | 45s to 1min | Removes the silver |
| Wash | 1.5 to 3min | Clears residual chemistry |
The developer reacts with dye couplers built into the paper, forming the cyan, magenta and yellow dyes that combine into every colour in the print. It is the temperature-critical step. The bleach-fix then strips out the silver and leaves only those dyes, so the print is light-safe once it is through that bath.
Light before the bleach-fix will fog the print
Leave the lights off until the print is fully through the bleach-fix bath.
Setting the exposure
Balance exposure first, then colour. Stop the lens down about two stops from wide open, which gives a sharp image and workable times. Then find the base exposure with a test strip. Give one sheet a range of times, say 5, 10, 15 and 20 seconds, then compare them after processing. As you are working blind, mark the strip's position and plan the times before darkness.
Changing the enlarger height means starting again
Once you start testing, leave the enlarger height alone. It alters the image size, the exposure and the colour balance all at once.
Balancing colour with filters
A colour enlarger carries three dichroic filters: yellow, magenta and cyan. Each subtracts its own colour from the light before it reaches the paper. The six hues of the colour wheel form three opposite pairs, and each filter slides the print along one of those axes.
The catch is that a filter works by removing its colour. Raise a filter and the print moves toward the opposite colour. Increase the yellow filtration and you take yellow out of the light, so the print goes bluer. Reduce it and the print warms up again.
Every correction on this page changes the filtration, not the colour on the paper. So a print that looks too yellow needs more yellow filtration, which takes the yellow out. This is the first thing that confuses almost everyone new to colour printing.
Why only two filters
Dialling in equal amounts of all three filters removes light evenly. It adds neutral density, lengthening the exposure without changing the colour. So any balance set with three filters can be matched by two, by subtracting the smallest value from all three. Printers leave cyan at zero and work with yellow and magenta alone.
Reaching every colour with two dials
Those two dials still cover the whole wheel:
- Yellow moves the print between yellow and blue.
- Magenta moves it between magenta and green.
- The third axis, red to cyan, is the diagonal between those two. Change yellow and magenta together: raise both toward cyan, lower both toward red.
That gives a simple rule for correcting a cast in a neutral tone such as a grey or a skin tone:
| Print looks too... | Do this |
|---|---|
| Yellow | Increase yellow filtration |
| Blue | Decrease yellow filtration |
| Magenta | Increase magenta filtration |
| Green | Decrease magenta filtration |
| Red | Increase yellow and magenta filtration |
| Cyan | Decrease yellow and magenta filtration |
Finding your balance
Start around Y = 90, M = 90. The right starting point varies between enlargers, and your paper box may suggest values. Correct one dial at a time, in steps of about 10. Note every setting. A logged balance is one you can repeat on the next print. A large filter change also shifts the exposure, so re-check density afterwards.
Judging the result
Assess a print only once it is washed, and always under the same white, daylight-balanced light. The same print reads warm under tungsten and cool under daylight. Judge under mixed light and you will chase a cast that is not there.
Always dry a print before you judge its colour or density. Prints dry slightly lighter and a little warmer than they look wet. A wet print will mislead you every time, so dry each test before deciding what to change.
With exposure and colour dialled in, make any extra copies now while the enlarger is still set up. Next, we'll wash and dry the prints so they last.