Mordançage: The Chemistry and Craft of Photographic Emulsion Manipulation

If you've ever wanted to literally peel apart a photograph and rebuild it with your hands, mordançage might be the most fun way to do it. This historic alternative process doesn't just alter images – it transforms them into three-dimensional objects through a dance of copper ions, hydrogen peroxide, and carefully controlled chaos.

The name comes from the French textile term “mordant”, meaning “to bite”, and that's exactly what happens. The chemistry literally bites into the photograph, dissolving the molecular bonds that hold silver particles within the gelatin matrix. What emerges is something between photography and sculpture – an image that can be lifted, draped, and manipulated like fabric.

A Process Born in the Lab, Raised in the Darkroom

The story begins in 1897 with German chemist Paul Liesegang, who documented what he called the “etch-bleach” process. He wasn't trying to create art – just looking for a better way to do film reversal. But chemistry has a way of surprising us. The following year, Momme Andresen swapped in hydrogen peroxide and hydrochloric acid, unknowingly setting the stage for what would become an artistic revolution.

Then… nothing. For over 60 years, as far as I can tell, the process collected dust in technical manuals.

Enter Jean-Pierre Sudre, a French photographer who in the 1960s saw artistic potential where others saw only chemistry. Working from his research center in Lacoste, Sudre made a crucial modification: replacing citric acid with glacial acetic acid. This single change transformed a technical curiosity into a controllable artistic medium. By 1967, his mordançage works were hanging in MoMA's “A European Experiment” exhibition, introducing American audiences to this alchemical process.

The knowledge transfer has been remarkably direct. Elizabeth Opalenik learned from Sudre himself in 1991, developing her signature “draping effect” and becoming the process's primary torch-bearer.

The Chemistry: What Iis Actually Happening in That Tray

Let's dive into the molecular madness. Mordançage orchestrates three simultaneous chemical processes that would make any chemist grin: silver oxidation, gelatin degradation, and selective emulsion lifting.

The Oxidation Cascade

The star of our chemical show is copper(II) chloride, which acts as an electron thief:

Cu²⁺ + Ag⁰ → Cu⁺ + Ag⁺

This reaction strips electrons from metallic silver particles, converting them to ionic silver – essentially bleaching your photograph. But copper(I) wants to return to its oxidised state. Enter hydrogen peroxide, our supporting actor:

2Cu⁺ + H₂O₂ + 2H⁺ → 2Cu²⁺ + 2H₂O

This regeneration creates a catalytic cycle where copper ions can repeatedly attack silver particles. Meanwhile, the silver ions aren't just floating around – they're forming complexes with chloride ions (Ag⁺ + Cl⁻ → AgCl), creating soluble species that wash away.

The glacial acetic acid isn't just there for kicks – it maintains a pH around 2-3, which is thermodynamically essential for the copper system's oxidizing potential. Without this acidity, the whole reaction grinds to a halt.

The Gelatin Transformation

Here's where things get weird and wonderful. Photographic gelatin normally sits happy at its isoelectric point (pH 4.8), maintaining a stable protein structure. Drop it into our acidic mordançage solution, and all hell breaks loose:

Gelatin-NH₂ + H⁺ → Gelatin-NH₃⁺

Those positive charges create electrostatic repulsion along the protein chains – imagine every part of the protein suddenly trying to get away from every other part. The result? The gelatin swells to 5-10 times its original volume.

Simultaneously, hydrogen peroxide is attacking the protein backbone, cleaving peptide bonds and weakening the entire structure. This one-two punch of swelling and degradation creates those characteristic “veils” – sheets of emulsion that literally float off the paper.

Shadows Lift First

The process preferentially attacks the darkest parts of your image. Why? Dark areas contain more metallic silver. More silver means more ionic products, creating localised chemical chaos that destabilises the emulsion. Your highlights, with their lower silver content, stay relatively intact while your shadows become sculptural elements.

The Hot Water Bath: Where Chemistry Meets Craft

After the chemical treatment comes a crucial step that many overlook: the hot water bath. This isn't just rinsing – it's creating a specific physical state where artistic magic happens.

At higher temperatures (40-50°C), the chemically-altered gelatin undergoes a phase transition from rigid gel to fluid sol. Think of it like butter melting – suddenly what was solid becomes workable. The gelatin, already swollen and partially degraded, becomes pliable enough to lift, drape, or remove entirely.

This temperature is importal. Too cool, and the gelatin stays rigid. Too hot, and your entire emulsion might dissolve into soup. You're looking for that Goldilocks zone where the emulsion becomes like wet fabric – moveable but intact.

Chemical Cleanup and pH Recovery

The hot water serves double duty, extracting residual copper chloride, silver complexes, and excess acid from the emulsion. Temperature accelerates diffusion – those unwanted chemicals flee the gelatin matrix much faster in hot water than cold. You're also starting to normalise the pH, pulling the gelatin back from its extreme acidic state.

Modern Materials: Not All Papers Are Created Equal

Today's mordançage artists have options Sudre never dreamed of, but understanding how different papers respond to the chemistry is crucial.

Ilford Multigrade papers remain the gold standard. Both fiber-based and resin-coated versions work, though fiber-based papers allow more dramatic effects due to how the emulsion integrates with the paper fibers. Sometimes, you may need to do a second pass with RC paper - i.e, first weaken the gelatin with the Mordençage solution and hot water processes, then do it again.

Foma papers bring their own character. Fomabrom Variant III FB performs similarly to Ilford, while the Fomatone series introduces warmtone characteristics that affect your final palette. These Czech-made papers use different gelatin formulations, so expect to adjust your timing. In my experience, Foma emulsion has a much weaker adhesion than Ilford, even for Fomaspeed RC paper. It just comes off, very easily, unlike, e.g, Ilford MGRC Pearl which often takes a second pass.

Bergger Prestige papers represent the high-end option. Artist Ingrid Dorner's stunning 2024 mordançage works specifically utilise Bergger substrates. These papers (likely contract-coated by Harman/Ilford) offer exceptional quality with neutral or warm tone options.

The Question of Colour

Here's something interesting: despite decades of experimentation, there's no documented successful mordançage on C41 color films or RA4 color papers. The chemistry tells us why.

Color materials create images through dyes, not silver particles. During C41 processing, color couplers react with oxidised developers to form cyan, magenta, and yellow dyes. The silver that was there gets bleached away entirely during normal processing. No silver, no mordançage – the copper ions have nothing to oxidise.

That being said, if one performs a bleach bypass during C41 development (i.e, skips the bleach to leave the silver), mordençage effects can occur, with artists such as Ella Morton active on using this technique, in combination with film soup, to make stunning alien-landscapes forged in extreme conditions and locations.

For RA4, there is the double whammy - a real lack of silver in the paper to begin with, and the adhesion layer is notoriously hard to break down. That being said - I have been experimenting with getting it to work - stay tuned!

The Recipe

After decades of refinement, the standard formula stands as:

• Copper(II) chloride: 10g/L (your primary oxidiser)
• Glacial acetic acid: 50ml/L (pH control and gelatin swelling agent)
• Hydrogen peroxide (35%): 30ml/L (secondary oxidiser and gelatin softener)
• Distilled water: to 1000ml total

Want more control? Adjust your concentrations. Higher copper chloride accelerates silver oxidation but risks over-bleaching. More hydrogen peroxide creates softer gelatin but might cause excessive lifting. Temperature matters too – reactions speed up with heat, but go above 22°C and you risk uncontrolled degradation.

The solution is surprisingly long lasting, and prepared solutions are known to last months after first use, simply by adding a dash of hydrogen peroxide at the beginning of a session to ‘wake it up’.

Some practitioners substitute copper sulfate for chloride, which changes reaction kinetics and shifts your final colours.

⚠ Safety

Mordançage involves seriously hazardous chemicals. That 35% hydrogen peroxide? It can cause severe chemical burns. Combine it with glacial acetic acid, and you've got corrosion hazards and respiratory risks from vapor exposure.

Essential safety gear:

• Chemical splash goggles (not safety glasses – splashes go around those)
• Acid-resistant gloves (nitrile minimum, neoprene better)
• Respiratory protection if your ventilation isn't excellent
• Access to an eyewash station within 50 feet

Environmental responsibility matters: Copper compounds are toxic to aquatic life and bioaccumulate in the food chain. Silver-containing solutions exceed regulatory disposal limits. This isn't stuff you pour down the drain – professional hazardous waste disposal is the only responsible option. You can try to neutralise it first with, e.g, washing soda.

The Contemporary Renaissance

After 125 years of mostly empirical practice, science is finally catching up. In 2019, researchers Fudala and Jones at George Mason University used scanning electron microscopy and X-ray spectroscopy to document exactly what's happening at the molecular level, confirming what practitioners have long observed about fiber-based paper superiority and silver content effects.

Today's artists are pushing boundaries Sudre never imagined. Brittany Nelson incorporates mordançage into large-scale digital prints exploring queer identity. Cara Lee Wade uses it to deconstruct fashion magazine imagery and beauty standards. These aren't nostalgic recreations – they're contemporary statements using historical chemistry.

The process's revival during photography's digital transition speaks to something deeper than mere novelty. In an age of infinite perfect copies, mordançage creates genuinely unique objects. Each piece is unrepeatable – the product of specific chemical conditions, timing, temperature, and the artist's physical intervention at the exact right moment.

Why This Matters Now

Mordançage exemplifies something we're losing in our digital age: the intersection of deep technical knowledge and intuitive artistic practice. You need to understand the chemistry to control it, but you also need to feel the exact moment when the gelatin releases under your fingers in that hot water bath.

From Liesegang's laboratory notebooks to contemporary gallery walls, mordançage demonstrates how historical processes remain relevant not through nostalgia, but through their unique expressive possibilities. The process demands respect – for its chemical hazards, certainly, but also for its potential to transform static photographs into dynamic, dimensional artworks.

As photography continues its digital evolution, mordançage reminds us that some artistic visions require getting your hands wet, literally. It's a process where chemistry becomes choreography, where scientific understanding enables artistic expression, and where a 125-year-old technique still has something new to say.

The magic isn't just in the chemistry – it's in that moment when you lift a veil of emulsion from the paper, watching an image transform from two dimensions to three, from fixed to fluid, from photograph to something entirely other. That's the real reaction happening in the tray: the transformation of scientific process into artistic possibility.