Gum Bichromate: The Pictorialist Process, Without the Dichromate

Gum bichromate is a pigment-based photographic printing process: you mix a pigment, gum arabic and a light-sensitive salt, brush it on, expose it under a negative, then develop in water. The result — velvety matte surface, pigment grain, a painter's touch — made it the weapon of the Pictorialists in the late 19^th century. Its only flaw fits in one word: the salt used, dichromate, is carcinogenic.

A process invented in 1855, revealed by Demachy

The principle — bichromated gum hardens in light — was established by Alphonse Poitevin in 1855. It stayed marginal until the 1890s, when Robert Demachy, in Paris, turned it into a genuine artistic medium. In 1895 his first gum prints, shown in Paris, London and Brussels, were received as a revolution: at last a photograph that looked like a drawing, where the hand intervenes. Demachy became its "apostle".

Dichromate gum · 1904

same process · different chemistry

Aquaprint · dichromate-free

Two monochrome gum bichromate prints a century apart: same matte surface, same pigment grain, different chemistry. We don't recreate Demachy's image — we carry on his process.

The masters who carried it

Gum bichromate is not a laboratory curiosity: it was the process of a whole generation of artist-photographers. Almost every Pictorialist master practised it — and all of them are in the Maison Picturale library.

Gum, by those who made it

A few period prints, monochrome and sanguine, from the masters' archive. Each links to its page in the Maison Picturale library.

Sanguine

Monochrome

Monochrome

Sanguine

Monochrome

Monochrome

Historical gum bichromate prints (public domain). Click to enlarge.

The truth: dichromate

What makes historical gum problematic is neither the pigment nor the gum arabic — it is the potassium or ammonium bichromate (dichromate) that makes it light-sensitive. The hexavalent chromium it contains is a proven carcinogen and mutagen (CMR), toxic by inhalation and a skin sensitizer. You can admire the genius of the process without wanting to handle that salt at home.

Aquaprint: gum, reformulated without dichromate

Aquaprint is our reformulation of gum bichromate. The gesture, the gum arabic, the pigment, the water development, the look: all preserved. Only the sensitizer changes: the VP formulation is without bichromate. That difference does not replace handling precautions: consult each product's safety information and the relevant safety data sheet (SDS) when available before use.

Gum, without bichromate

Same process, same look, different chemistry. Aquaprint takes up the gum-print gesture in a VP formulation without bichromate. Consult each product's safety information and the relevant SDS when available before use.

Formulation

VP system — bichromate-free

Safety

Read product instructions and SDS

Look

Matte surface, pigment grain, multiple layers

Practice

Workspace prepared to product instructions

Aquaprint Sanguine kit· €79Or acquire a master print →

The three Aquaprint gums

Gum bichromate is not a single colour: it is a family. Aquaprint offers three — all with the sensitizer, dichromate-free.

Sanguine

Sanguine is a precise gum variant: a red-brown pigment evoking the red chalk of Old Master drawings. Demachy made it famous, his red gums recalling Renaissance sanguine drawings. Aquaprint Sanguine follows exactly that path.

Dichromate sanguine · 1898

same sanguine · different chemistry

Aquaprint Sanguine · dichromate-free

Demachy's sanguine (1898) and today's Aquaprint Sanguine: the same red chalk, without the dichromate.

Four-colour

Where Pictorialists mostly stayed monochrome, gum also lends itself to colour: several pigmented passes (cyan, magenta, yellow, black) are stacked. Aquaprint Quadrichromie takes gum all the way to a full colour image — still dichromate-free.

FAQ

Does Aquaprint really give the same look as dichromate gum?
Yes. Dichromate is only a hardening trigger; it plays no part in the final image. The matte surface, the grain and the ability to stack layers are identical.

Can you work in colour, like four-colour gum?
Yes: you superimpose several pigmented passes (cyan, magenta, yellow, black), exactly as in traditional gum — without dichromate.

Which precautions are required?
VP Aquaprint is formulated without bichromate, but it remains a photographic-chemistry practice. The VP N°03 developer is harmful if swallowed and skin contact must be avoided. Wear the indicated protection and consult the safety information, then the relevant SDS when available, before handling.

For the full panorama of alternative processes, see our guide to alternative processes or the glossary.

Further reading: the beginner Aquaprint tutorial · fixing a failed print · the Aquaprint process