Historical context
Cyanotype is the blue Prussian-blue print invented in 1842 (see the cyanotype guide). Printers have long changed its colour by bleaching the blue away and then re-colouring the image with a tannin. The chemistry is simple: the print is exposed in turn to an alkali and a polyphenol. We have found no reliable source for who first did this, so we give no inventor or date.
What it is and how it differs
- A post-processing step. Toning is done on a finished, washed and dried cyanotype. The sensitiser, exposure and washing stay as in the cyanotype or New Cyanotype guides.
- Bleach, then tone. A weak alkali (sodium carbonate, or washing soda) bleaches the blue to a pale yellow-brown. A tannin bath then restores a dark image. Practitioners disagree on order: some bleach then tone, some tone then bleach, some bleach, tone and bleach again (Ray Harris, AlternativePhotography.com).
- Unpredictable. Godman calls toning "by no means an exact science". Exposure, paper, tannin source and bleaching time all change the result. Keep notes.
- One-way. The original blue cannot be recovered once bleached.
Materials and chemistry
| Role | Material | Notes |
|---|---|---|
| Bleach | Sodium carbonate (washing soda) | "Not caustic soda" (Harris). Hypochlorite household bleach was once used, but van Keuren calls sodium carbonate odourless and more effective. |
| Tannin | Tannic acid powder, strong black or green tea, instant coffee | Tea gives a warmer, yellower tone than pure tannic acid but is more likely to tint the paper whites (van Keuren). |
Published recipes
| Recipe | Quantities | Source |
|---|---|---|
| Bleach | 1 teaspoon sodium carbonate per litre of water; 15 to 30 seconds | Harris |
| Tea toner | 5 or 6 tea bags in warm water, strong and dark brown; soak about 15 minutes | Harris |
| Tannic acid sequence | Tannic acid about 1/2 teaspoon and sodium carbonate about 1/2 teaspoon, each per quart (about 1.1 litres) of water | van Keuren |
| Brown toning | Tannic acid 1 g per 100 ml, dip 5 to 10 seconds, rinse; then sodium carbonate 1 g per 100 ml until the colour appears; wash at least 5 minutes | Godman |
| Coffee toner | A teaspoon or two of instant coffee in a litre of water (the author's preference) | Godman |
Godman's 1 g per 100 ml solutions are stronger than the others (roughly twice Harris's bleach, taking a level teaspoon as about 5 g, and several times van Keuren's), so test on a spare print and shorten times accordingly. For wine, the cyanotype article on AlternativePhotography.com suggests only that you experiment with tea, coffee or wine; no quantities are published there, so follow a reference for any wine recipe.
What to expect
- Split tones. A continuous-tone print often bleaches unevenly, giving grey highlights with blue shadows or yellow highlights with green shadows (van Keuren).
- Rosy-brown. Tannic acid restores lost tones in a rosy-brown. Partial bleaching followed by toning gives a duotone with rosy-brown highlights and blue shadows (van Keuren).
- Paper and exposure matter. Van Keuren reports richer bleached colours from overexposing on a soft paper such as BFK Rives.
- Brown overall. Harris's tea method shifts the blue to brown; subtler browns come from less toning or weaker solutions.
Procedure
- Print and wash a cyanotype in the normal way, and let it dry so it has fully oxidised. Use unbuffered paper: Ware warns that alkalis are hostile to cyanotype chemistry, so the paper must tolerate the carbonate bath.
- Bleach. Immerse in the sodium carbonate solution. Plunging the print into water stops bleaching at any point, and the stopping point sets the shade of blue, green or yellow (van Keuren). Partial bleaching gives split tones, such as grey highlights with blue shadows.
- Rinse thoroughly after bleaching.
- Tone. Immerse in the tannin bath until the colour you want appears. Darkening continues during washing and drying, so lift the print before it reaches the desired effect (van Keuren).
- Wash and dry. A final wash of at least 5 minutes is recommended (Godman), then dry flat or on a rack.
- Local effects. Brush bleach onto a dry print and flood with water for hard edges, or onto a damp print for soft edges (van Keuren).
Looking after toned prints
Toned cyanotypes still carry the weaknesses of the base print. Alkali attacks Prussian blue (Ware), so keep time in the carbonate bath short and rinse it out thoroughly. Record the recipe, times and paper for each print so you can repeat a colour you like (Godman, Harris). Toning solutions can be reused if stored in plastic bottles in a cool place (Godman), but van Keuren advises discarding tannic acid, which does not keep.
Troubleshooting
| Problem | Likely cause | Remedy |
|---|---|---|
| Stained highlights | Tannin tints the paper; strong tea is worse | Use weaker or shorter tannin baths; accept some tint (van Keuren) |
| Colour not as expected | Order of steps, paper, exposure, tannin source | Keep notes; change one variable at a time (Harris) |
| Brittle paper | Hypochlorite bleach shortens fibres | Use sodium carbonate; wash until no bleach smell (van Keuren) |
| Weak, muddy image | Over-bleached or toned too long | Stop bleaching earlier; lift the print early |
| Print fades later | Washing and light | Re-oxidation in the dark for 2 to 4 weeks restores a faded cyanotype (Bostick & Sullivan) |
Safety
Toning chemistry is mild but not harmless. Sodium carbonate is an eye irritant, and tannic acid powder stains the skin. Wear gloves and eye protection, keep the baths away from food, and wash your hands after handling prints.
| Chemical | Hazards |
|---|---|
| Sodium carbonateWarning | Causes serious eye irritation. |
| Potassium ferricyanideWarning | Causes serious eye irritation.; Toxic to aquatic life with long lasting effects. |
| Hydrogen peroxideDanger | May cause fire or explosion; strong oxidiser.; Harmful if inhaled.; Harmful if swallowed.; Causes severe skin burns and eye damage. |
Classifications from the European Chemicals Agency (official EU classification where one exists, otherwise the one agreed by REACH registrants or most often notified). Read the safety data sheet that comes with your chemicals, and dispose of them in line with local regulations.
- Sodium carbonate is classed as an eye irritant (H319).
- Tannic acid stains skin and slightly stains white paper areas (van Keuren, Harris); wear gloves. It is not in our chemicals database, so check the supplier's safety data sheet.
- Hydrogen peroxide is sometimes used to speed up oxidation before toning. Use only pharmacy-strength 3% (Bostick & Sullivan dilute 100 ml of 3% to 1 litre). Concentrated grades are corrosive oxidisers, and above 12% it is a regulated explosives precursor in the UK.
- Other published toners. Godman also describes ammonia bleaches and a 5% lead acetate toner, which he calls "quite toxic". We have not reproduced those recipes because we do not hold hazard data for them.
- Spent baths. Van Keuren recommends discarding the tannic acid and carbonate trays after the session, since tannic acid does not keep.
Further reading
Christina Z. Anderson, Cyanotype Toning (Routledge). A whole book on the subject.
Mike Ware, Cyanomicon. Free from mikeware.co.uk; covers cyanotype chemistry and permanence.
See also cyanotype on fabric.
Sources
- Cyanotypes: how blue can you get?, Ray Harris, AlternativePhotography.com
- A Non-Silver Manual: Cyanotype, Sarah van Keuren, AlternativePhotography.com
- Cyanotype, Malin Fabbri, AlternativePhotography.com
- Toning a Cyanotype, Lloyd Godman
- Simple Cyanotype workshop notes, Mike Ware
- Cyanotype Kit Instructions, Bostick & Sullivan
- ECHA CHEM substance record: Sodium carbonate, European Chemicals Agency (hazard classification, via the Silverlog chemicals database)
- ECHA CHEM substance record: Hydrogen peroxide, European Chemicals Agency (hazard classification, via the Silverlog chemicals database)