Color Venn

When you calibrate a cyanotype, a 25-gray target is enough. The process has only one pigment, you measure its response, you output a curve. When you calibrate an Aquaprint Color in CMYK or a colour carbon print — also calibrated in CMYK — it's no longer the same — you have several pigments overlapping, and the gray target tells you nothing about their interactions. You can have a flawless Cyan, a flawless Magenta, a flawless Yellow, and still end up with a print where the overlaps are muddy because your pigments don't mix the way you expected.

The Color Venn solves this by building the overlaps into the target itself. Instead of measuring each pigment in isolation, you measure the real mixes — Cyan + Magenta = Blue, Magenta + Yellow = Red, Cyan + Yellow = Green, and the triple intersection at the center that should give you your densest Black. Seven zones to measure, seven responses, and you output a complete calibration of your CMYK printing from a single target.

#What you see

This screen was retired from the app on August 31, 2026: it won't come back. What's available instead is the site's free generator — three Cyan, Magenta, Yellow circles overlapping in a triangle, their intersections naturally producing the secondary colors. You'll find it on the gum bichromate calibration and carbon calibration pages: a preview shows on screen, a button downloads the PNG.

That PNG (A4, 300 dpi, computed right in your browser, no sign-up) prints exactly like a classic gray target — on transparency, with no color management (see printing without color management). Once exposed and then printed on your sensitized paper, you get a physical target with the seven color zones to compare.

There's no automatic scan-based measurement for the Color Venn today — compare the seven zones by eye (see The test below) rather than relying on an automatic reading in the app.

#Why it matters

For Aquaprint CMYK. Without Color Venn, calibrating an Aquaprint CMYK means printing four separate neutral targets (one per channel), measuring them independently, and hoping the corresponding curves add up correctly on the final print. Spoiler: they don't always add up. With Color Venn, you measure directly what the overlap produces, so your calibration reflects the reality of your process and not a theory.

For colour carbon printing. Like Aquaprint, the app calibrates it in CMYK — four transfers C/M/Y/K, never a CMY trichrome without a separate black. If you calibrate each pigment in isolation with a gray target, you have no idea of the final black's density — you only discover it after a full series of transfers. With Color Venn, you measure it from the first test target. Vision Picturale currently only sells a Charbon Mono kit (in production, not yet for sale): for colour pigment printing, its Aquaprint kits are what's available; Maison Picturale can print colour carbon on request.

As a teaching tool. Even if you only do monochrome, looking once at a printed and exposed Color Venn makes you understand concretely what CMYK printing is. The intersection zones are no longer print-shop manual theories — you physically see how the pigments combine on your paper.

#When you don't need it

For monochrome processes. Cyanotype, platinotype, Charbon Mono, Aquaprint Sanguine, bromoil, gumoil — a single pigment, no overlap. The 25-patch gray target is the right tool. The Color Venn adds nothing.

If your contact press can't hold the precision. Aquaprint CMYK and colour carbon printing both demand tight registration between layers — pouches or transfers that don't line up ruin the result even if every pigment is calibrated. If your equipment can't physically hold that precision, calibrating with a Color Venn is pointless — what's limiting you is the mechanics, not the chemistry.

If you're starting out in alternative processes. The Color Venn generator on the site is free and available to all, but requires technical expertise. Master monochrome cyanotype calibration plus Aquaprint Monochrome with a classic gray target before investing in CMYK. Count five to ten clean monochrome prints minimum.

#Key facts

#The test

Generate a Color Venn on the site's generator (A4 PNG, 300 dpi). Print it on an inkjet transparency, with no color management. Lay the transparency on a sheet of white paper in daylight. You should distinctly see the seven colored zones — pure Cyan, pure Magenta, pure Yellow, and the three double overlaps, plus a near-black zone at the center formed by the overlap of all three. If one of the seven zones doesn't appear or the colors are muddy, the printer applied a parasitic correction — reread the page on printing with no color management.