Guide
Making digital negatives for cyanotype, Van Dyke, salt and platinum prints
Alternative photographic processes like cyanotype, Van Dyke brown, salt prints and platinum need a negative as large as the final print, because they are contact printed under UV light or sunlight. Today most printers make those negatives digitally: invert the photo, apply a curve that suits the process, and print it on transparency film. This tool prepares such negatives with process-specific starting curves, calibration aids and exact print sizing.
Why a plain inversion is not enough
Each process responds to light differently. Cyanotype has a short tonal range and blocks up in the shadows; platinum is long and gentle. A straight negative prints with muddy or blown midtones. The curve lifts or lowers midtones and adjusts contrast, so the tonal scale of the photo lands where the chemistry can reproduce it.
Starting curves for each process
Pick the process to load a sensible starting point: silver gelatin contact printing, cyanotype, Van Dyke brown, salt print, or platinum/palladium. Cyanotype starts with strongly lifted midtones and reduced contrast; platinum with only slight adjustments. These are starting points, not calibrations; paper, chemistry, UV source and film all shift the result.
Midtones and contrast
Midtones brighten or darken the middle of the tonal range on the final print. Contrast steepens or flattens the overall curve. Make changes in small steps, print a test strip, and judge the dried print, since many processes dry down darker.
Density limits
“Darkest ink” sets how dense the negative gets where the print should be paper white. Too little density and highlights print gray; too much wastes exposure time. “Clearest film” sets how transparent the film stays where the print should reach maximum black. Set both from your calibration print.
The 21-step wedge
Switch on the calibration wedge to add a strip of 21 gray steps alongside the image. After printing, the steps show exactly where the curve compresses or loses tones. Adjust until each step is visible on the print, and note the settings for that paper and process.
Mirroring
For the sharpest contact print, the ink side of the film should touch the sensitized paper. Mirroring the negative makes the print read correctly in that orientation. It is on by default; switch it off only if you place the film ink side up.
Size and resolution
Set the print width in inches or centimeters and the resolution; the height follows the photo. The default 360 pixels per inch matches the native resolution of many photo inkjet printers. The resolution is written into the saved file, so printing at 100 percent produces the exact physical size.
Practical workflow
Convert the photo to black and white first, adjust it to look good as a positive, then build the negative here. Print on transparency film with the printer’s color management off or set consistently, expose, process and compare with the wedge.
Keeping notes
Alternative processes vary with humidity, paper batch, coating technique and the age of the chemistry. Record the settings, exposure time and conditions for each print next to the wedge result. After a few sessions, those notes become your own calibrated curve, far more reliable than any generic preset.
Related tools
Prepare the monochrome positive with Grayscale Image. Plan exposure stops with the Darkroom Timer. To recreate toned looks digitally instead, try the Sepia Photo Filter.
Checked against the current version of the Digital Negative Maker on .