Colour Printing and Darkroom Practice
This section covers Colour Printing and Darkroom Practice: enlarger use, CMY filtration, test strips, RA-4 chemistry, print evaluation and darkroom discipline.
Core rules
- An enlarger has a lamp, condenser or diffuser, negative carrier, lens, aperture, focus control and easel. A condenser gives contrast and reveals dust; a diffuser is softer.
- Colour heads use dichroic cyan, magenta and yellow filters. Filtration is subtractive: adding a filter absorbs its complementary light and reduces that dye in the print.
- Exposure controls density; filtration controls colour balance. Change one, then recheck the other because they interact.
- RA-4 process: expose colour paper, develop, bleach-fix, wash, stabilise and dry. Temperature and time are critical, roughly 35–38 °C depending on chemistry. Use the specified safelight; colour paper is not safe under bright amber light.
- A test strip exposes a series of steps to find base exposure. A ring-around varies filtration around a known good print to judge colour direction.
- Evaluate a print after it dries; dry-down makes prints slightly darker and can shift colour.
- Dodging reduces exposure locally; burning adds it. Keep tools moving to avoid hard edges.
Worked example
A test print has a clear yellow cast. Reasoning: yellow in the print means too much yellow dye formed, so too much blue light reached the yellow-forming layer. Add yellow filtration to the enlarger head; the yellow filter absorbs blue and reduces yellow dye. Re-expose and compare. If the cast were magenta, add magenta filtration; for cyan, add cyan filtration. Do not fix colour by changing exposure alone, because that mainly changes density.
Traps
- Correcting a yellow cast by adding blue filtration, which increases yellow, instead of adding yellow filtration to reduce it.
- Forgetting that filtration changes exposure; a strong filter may need a time or aperture adjustment.
- Evaluating prints wet; dry-down changes density and colour.
- Contaminating chemistry or using exhausted bleach-fix, which causes colour shifts and stains.