Mordançage: The Honest Assessment of an Unsustainable Process

Part 7 of 13 in the Sustainable Darkroom series | ← Previous: Part 6 | Next: Part 8 →

This is the post where I have to be honest about a process I love that I can't really defend environmentally.

Mordançage—the technique of bleaching and lifting silver gelatin emulsions to create veiled, ethereal images—uses copper chloride. Copper is a heavy metal with significant aquatic toxicity. There's no botanical alternative, no eco-friendly reformulation, no way to make this process green.

What I can do is minimise the impact, be honest about the trade-offs, and explain why I continue to do it anyway.

What Mordançage Does

The process, perfected by Jean-Pierre Sudre in the 1960s, works in two stages:¹

Stage 1 (Bleaching): A silver gelatin print is immersed in a solution of copper chloride, glacial acetic acid, and hydrogen peroxide. The copper ions bleach the metallic silver, converting it back to silver chloride. Simultaneously, the acidic peroxide softens the gelatin in heavily-exposed (silver-rich) areas.

Stage 2 (Lifting/Redevelopment): When the print is transferred to water, the softened emulsion in dark areas lifts away from the paper base, creating veils. The print can then be redeveloped (restoring blacks) or left bleached, and the lifted emulsion can be manipulated, removed, or dried in place.

The result is something impossible to achieve any other way: an image that appears to be dissolving, with ghost-like veils floating above or away from the surface.

The Mordançage Formula

My working formula:²

• 10g copper(II) chloride
• 50ml glacial acetic acid
• 30ml 35% hydrogen peroxide
• Distilled water to 1 litre

The copper chloride is the bleaching agent. The acetic acid provides the acidic environment necessary for emulsion lifting. The hydrogen peroxide activates the copper and softens the gelatin.

The Environmental Problem: Copper

Copper is where this process fails environmentally.

Aquatic toxicity

The US EPA's freshwater criterion for copper is 2.3 μg/L—micrograms per litre.³ Copper is extraordinarily toxic to aquatic invertebrates, algae, and fish at concentrations far below what humans would notice.

For comparison, typical acute toxicity values (LC₅₀):

• Copper to Daphnia: ~10–50 μg/L (depending on water chemistry)
• Copper to sensitive fish species: ~17–200 μg/L
• Silver to Daphnia: ~0.6 μg/L

Copper is less acutely toxic than silver to most organisms, but still highly problematic. The mordançage working solution contains 10g copper per litre—roughly 4 million times the EPA criterion concentration.

No recovery method

Unlike silver, which can be recovered via steel wool displacement, copper in the mordançage solution exists as copper(II) chloride in acidic solution. There's no simple home method to recover it.

The copper could theoretically be precipitated as copper hydroxide by adding sodium hydroxide, but this produces a sludge that still requires hazardous waste disposal. You've changed the chemical form but not eliminated the problem.

Persistence

Copper is an element. It doesn't biodegrade. Once released into the environment, it remains indefinitely. Municipal wastewater treatment removes some copper (it partitions to sludge), but not all. What reaches receiving waters persists.

The Partial Mitigation: Reusability

One factor partially offsets the copper problem: the mordançage bleach is reusable virtually indefinitely.

When the bleach weakens (which you notice as slower bleaching times), you don't discard it. You simply add more hydrogen peroxide to reactivate the copper.⁴ The copper isn't consumed by the bleaching reaction—it cycles between Cu²⁺ and Cu⁺ states, with peroxide restoring the oxidised form.

I've been using the same litre of mordançage bleach for over a year, topping up the peroxide periodically. In that time, I've processed around 100 prints. If I were discarding and mixing fresh bleach each session, I'd have used 10+ litres of copper-containing solution. Instead, I've used one litre repeatedly.

This dramatically reduces the waste volume, though it doesn't eliminate it. Eventually the solution accumulates enough silver chloride, gelatin fragments, and degradation products that it must be discarded.

The Silver Byproduct

The copper chloride bleaches silver, producing silver chloride that precipitates as white sludge. This accumulates in the bleach bath and can be collected when the solution is eventually discarded.

I strain my exhausted mordançage bleach through a coffee filter to capture the silver sludge. This:

• Recovers the silver (which has modest value and definitely has environmental impact if released)
• Separates the copper solution from the silver precipitate
• Makes disposal slightly less problematic (though the copper solution still requires proper disposal)

The silver sludge can be combined with other silver waste for eventual refining. The copper solution goes to hazardous waste.

Honest Accounting

Let me calculate the actual impact of my mordançage practice:

Initial investment: 10g copper chloride to make 1 litre of bleach (approximately 5g copper metal equivalent)

Prints made so far: ~100 mordançage prints from this batch

Per-print copper consumption: Essentially zero, because the copper isn't consumed.

This is the key point: the copper cycles between oxidation states during bleaching but is regenerated by hydrogen peroxide. I haven't added any more copper chloride since making the original batch. Every additional print I make reduces the amortised copper burden—if I eventually make 1000 prints from this litre before it degrades beyond use, the copper-per-print drops to 5mg. If I make 100, it's 50mg. The denominator grows; the numerator stays fixed.

Disposal: This is where I have to be honest—I haven't gotten around to proper disposal yet. The exhausted bleach is sitting in a labelled container waiting for me to take it to hazardous waste collection. This is not good practice, and I need to address it. But it also means my actual copper release to the environment so far is zero. The 5g of copper is still in that bottle.

Compared to other sources

Is this significant? Context helps:

• A single copper-bottomed pan degrades and releases copper over its lifetime
• Copper water pipes release copper continuously at low concentrations
• Fungicides used in agriculture release vastly more copper to the environment than all darkroom mordançage combined

My mordançage practice has so far released zero copper to the environment—the original batch is still in use. When I eventually dispose of it properly, the impact will be:

• Manufacturing of the copper chloride (already incurred)
• Processing at the hazardous waste facility
• Whatever imperfections exist in that processing

This is not zero impact, but it's not catastrophic either.

Compared to other darkroom processes

Process	Primary Heavy Metal	Annual Burden (my usage)	Disposal
B&W Fixer	Silver	~200–500g	Recovered
C-41/RA-4 Blix	Silver	~100–200g	Hazardous waste
Selenium Toner	Selenium	~5–10g	Hazardous waste
Mordançage	Copper	~5g (amortised over bleach lifetime)	Hazardous waste

Mordançage is in the same category as selenium toning—a genuine heavy metal concern, but at volumes that are manageable with proper disposal. The key difference is that the mordançage copper can be amortised over hundreds of prints, making the per-print burden very low if you maintain and reuse your bleach properly.

Why I Continue

Given all this, why do I still do mordançage?

Aesthetic necessity: There is no other way to achieve what mordançage achieves. No digital manipulation, no alternative process, nothing else produces the veiled, lifted emulsion effect. If I want that aesthetic, mordançage is the only path.

Controlled impact: By reusing the bleach indefinitely, I've reduced the material input to 10g of copper chloride over (so far) 100+ prints, with no disposal yet. The amortised burden continues to decrease with every print. When I eventually do dispose of the bleach, it goes to hazardous waste—so my actual release to the environment will be whatever imperfections exist in that processing chain.

Honest trade-off: I don't pretend this is sustainable. I accept that I'm using a toxic process because I value what it produces. The alternative would be to stop making mordançage prints, which would eliminate the impact entirely. I've chosen not to do that.

Context: I take public transport every day, I live in an apartment. The copper from mordançage is a real concern but exists within a broader context of choices and trade-offs. This isn't an excuse—it's a recognition that perfection isn't the standard.

How to Neutralise the Bleach

If you want to reduce the hazard before disposal (or before that overdue trip to hazardous waste collection), you can precipitate the copper out of solution:

Sodium hydroxide method:

Add sodium hydroxide (NaOH, available as drain cleaner or from chemical suppliers) to the exhausted mordançage bleach. The reaction:

CuCl₂ + 2NaOH → Cu(OH)₂↓ + 2NaCl

The copper precipitates as blue-green copper hydroxide, leaving sodium chloride (table salt) in solution.

Procedure:

1. Work outdoors or with good ventilation—the solution is still acidic initially
2. Slowly add NaOH solution (dissolve ~20g NaOH in 200ml water) to the mordançage bleach
3. Stir and allow to react—you'll see blue-green precipitate forming
4. Continue adding NaOH until no more precipitate forms and the solution tests alkaline (pH >10)
5. Allow precipitate to settle (this can take hours or overnight)
6. Decant the clear liquid (now mostly sodium chloride solution—much less hazardous)
7. The copper hydroxide sludge still requires proper disposal, but it's more stable and concentrated than the original solution

What this accomplishes:

• Converts soluble copper (high mobility, high aquatic toxicity) to insoluble copper hydroxide (low mobility)
• Neutralises the acetic acid
• Reduces the volume of material requiring hazardous waste disposal
• The supernatant liquid is primarily salt water and can be disposed of more easily

What this doesn't accomplish:

• The copper is still there—you've just changed its form
• The precipitate still needs proper disposal (hazardous waste or metal recycling)
• This isn't a licence to pour anything down the drain

Recommendations for Mordançage

If you're going to do mordançage:

1. Reuse the bleach

Don't mix fresh solution for each session. Top up with hydrogen peroxide as needed. One litre can last a year or more.

2. Collect the silver sludge

When you eventually discard the bleach, strain it and recover the precipitated silver chloride. This has value and definitely shouldn't be released to the environment.

3. Neutralise before disposal

Use the sodium hydroxide method above to precipitate copper hydroxide. This makes the solution less hazardous and concentrates the copper for easier handling. Do this before the solution sits around for too long (speaking from experience).

4. Dispose properly

The copper precipitate goes to hazardous waste collection. The neutralised supernatant is far less problematic but still benefits from proper disposal. Don't pour any of it down the drain—ever.

5. Work safely

Glacial acetic acid is corrosive. Hydrogen peroxide at 35% concentration can cause burns. Copper chloride is toxic. Wear gloves, work with ventilation, and don't store the solution in containers that could be mistaken for something else.

6. Accept the trade-off

If the environmental impact of mordançage is unacceptable to you, don't do mordançage. There's no way to make this process green. The only sustainable mordançage is no mordançage.

The Broader Point

This series has examined sustainable darkroom practice with the goal of identifying what actually matters. The hierarchy has been consistent: silver » water » chemistry » developer choice.

Mordançage doesn't fit neatly into that hierarchy. It introduces a heavy metal (copper) that isn't present in standard processing and can't be recovered at home. It's a genuine environmental cost with no mitigation beyond minimising volume and disposing properly.

The honest conclusion is that mordançage is not sustainable. It can be made less bad through reuse and proper disposal. But “less bad” isn't sustainable.

I continue to do it because I value the results more than I value perfect environmental virtue. That's a choice I make knowingly. Whether it's a choice you want to make is up to you.

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