Can you make gum bichromate without bichromate?

Yes. Vision Picturale reformulated gum bichromate as Aquaprint by replacing potassium bichromate with the universal sensitizer, a proprietary non-toxic formulation. The rest of the process is identical — gum arabic + watercolor pigment + sensitizer, water development — and the polychromatic painterly result is indistinguishable from the historical version. Only the chemistry changes, enabling home practice in a kitchen without a carcinogenic oxidizer.

Is potassium bichromate dangerous?

Potassium and ammonium bichromate, used in historical gum bichromate, are oxidizers classified as irritant, skin sensitizers and potentially carcinogenic (hexavalent chromium compounds). Handling them requires a ventilated studio, protective equipment and regulated effluent disposal. This is why Vision Picturale replaced them with the sensitizer in Aquaprint: you get the same result without that toxicity, working on a plain kitchen countertop.

How many colors can you layer in Aquaprint?

Aquaprint lets you layer as many color coats as you like, each adding one pigment. For a four-color print, you typically layer cyan, magenta and yellow (sometimes a black), i.e. three to four successive passes. Each coat is applied, dried, exposed and developed before the next. This layering produces a chromatic richness digital printing cannot reproduce, at the cost of precise registration between passes.

Do you need a special negative for Aquaprint?

Aquaprint needs a digital negative printed on transparent film, at the final print size (contact process, no enlargement). For color, you need a per-channel separation with one negative per pigment, calibrated to each color's response curve. The ICC profiles supplied with the Vision Picturale kit compensate for these curves. A well-densified negative is decisive: the gum's exposure window being narrow, a negative too light or too dense ruins the coat.

Gum Bichromate: Beginner's Tutorial

Gum bichromate (or "gum print") is one of the most expressive alternative photographic processes — polychromatic prints with a painterly richness close to watercolor. The historical recipe uses potassium or ammonium bichromate, an oxidizer classified as irritant and potentially carcinogenic. Not something you want to use at home.

At Vision Picturale, we reformulated this process under the name Aquaprint. Same painterly result, same color freedom, but using our sensitizer — no bichromate, no toxics, safe to practice in your kitchen.

Aquaprint vs. historical gum bichromate: what's different?

Aquaprint replaces potassium bichromate with the universal sensitizer, a proprietary non-toxic formulation. The rest of the process is identical: gum arabic + watercolor pigment + sensitizer, developed in water. The visual result is indistinguishable — only the chemistry changes, for your safety.

Materials for your first Aquaprint

An Aquaprint pouch — gum, pigment and sensitiser already mixed, 350 ml, in the Aquaprint CMYK kit
VP N°03 Developer — the bath that reveals and fixes the print
The colour of your choice — one pouch per hue (black, cyan, magenta, yellow, ochre, red…)
Watercolor paper 300 gsm minimum, no optical brighteners
A digital negative printed on transparent film
A UV source — direct sun or Luminograph

Step 1: Prepare the Aquaprint emulsion

Pour the pouch into a bowl: gum, pigment and sensitiser are already mixed, there is nothing to measure out. Work under incandescent light — the emulsion is UV-sensitive.

Step 2: Coat the paper

Apply a uniform coat using a flat brush or hake. Dry completely in the dark (30–45 minutes at room temperature).

Step 3: Expose to UV

Place your negative in contact with the paper under glass. Expose to UV — typically 3–8 minutes with a Luminograph, 2–5 minutes in direct summer sun.

Step 4: Develop in water

Immerse in a room-temperature water bath. Unexposed areas dissolve gradually in 10–30 minutes. Do not force — let the water work.

Step 5: Additional color passes

Once dry, re-coat with a second color. Layering cyan, magenta and yellow produces a richness that digital printing simply cannot replicate.

Learn more on the Aquaprint process page or order the Aquaprint CMYK kit directly.

Further reading: the history and chemistry of Aquaprint · fixing a failed print · the guide to alternative processes

Gum Bichromate: Making Your First Print — Without Bichromate, With Aquaprint