Cyanotype

Historical Context

Invented by Sir John Herschel in 1842, cyanotype was the first successful non-silver photographic printing process. Anna Atkins used it to create the first photographically illustrated book, British Algae: Cyanotype Impressions (1843-53). The process later became commercially important as the "blueprint" for reproducing architectural and engineering drawings.

Chemistry

The traditional cyanotype uses two solutions that are mixed immediately before coating:

Solution A — Ferric Ammonium Citrate (green form)

Solution B — Potassium Ferricyanide

Working Solution: Mix equal parts Solution A and Solution B immediately before use.

Shelf Life: Store each stock solution in a brown bottle in the dark. Solution B keeps well; Solution A is prone to mould, sometimes within a week or two, so discard it if it turns cloudy or grows mould. The mixed sensitiser only lasts a short time, so mix it shortly before coating.

Procedure

1. Paper preparation: Select appropriate paper. No pre-treatment is typically required for traditional cyanotype.

2. Coating: Under subdued tungsten light (not fluorescent or daylight), mix equal volumes of Solutions A and B. Apply to paper with brush or rod. Coat evenly, avoiding puddles.

3. Drying: Dry coated paper in darkness. Can be force-dried with gentle heat (hairdryer on low) but air drying produces more consistent results. Paper turns from yellow-green to grey-green when dry.

4. Exposure: Place negative in contact with sensitised paper, emulsion to emulsion. Expose to UV light. Exposure times vary enormously depending on light source:

   • UV lamp: Ware gives around 20 to 30 minutes
   • Sunlight: much shorter than a lamp in strong sun and much longer under cloud. It varies with season, sky and negative density, so make a test strip rather than trusting a figure

5. Judging exposure: Traditional cyanotype must be heavily overexposed. Keep exposing until the deepest shadows have reversed, turning lighter and greyish (sometimes bronzed), and the image looks 'blocked up'. It will look washed out, but darkens after washing.

6. Processing: Wash the print face down in gently running water (or several changes of still water) until no yellow remains in the highlights; Ware says 20 minutes should suffice. Some loss of blue during washing is normal. Wash water must not be alkaline, as alkali bleaches Prussian blue.

7. Oxidation: Full blue colour develops during drying. Can be shown immediately by soaking the print for about half a minute in 0.3% hydrogen peroxide during the final wash. Ware notes this makes no difference to the final dried density, so it isn't necessary.

8. Drying: Air dry or blot and dry flat.

Contrast Control

The traditional cyanotype has inherently high contrast. Methods to modify:

• Ammonium dichromate: Ware's traditional recipe contains none (his New Cyanotype has 0.1 g per 100 ml). Some practitioners add a trace to raise contrast, but traditional cyanotype rarely needs it. Ammonium dichromate is a Category 1B carcinogen and a REACH Annex XIV substance (see the warning under New Cyanotype below); use citric acid or negative choice instead where you can.
• Citric acid: Ware suggests that dilute citric acid in the first wash bath may improve the image
• Exposure manipulation: Overexposure followed by reduction in weak sodium carbonate can compress highlights
• Paper selection: Softer papers produce lower contrast

Toning

Traditional cyanotype can be toned to alter colour:

Tannic acid toning (produces blue-black to purple-black tones)

1. Bleach in weak sodium carbonate until blue converts to yellow
2. Rinse thoroughly
3. Immerse in a tannic acid solution until the desired colour is achieved (published recipes run from about 1/2 teaspoon per quart to 1 g per 100 ml, so start weak and see the cyanotype toning guide)
4. Rinse and dry

Tea/Coffee toning (produces warm brown-blacks)

Same bleaching process, then immerse in strong tea or coffee solution.

For more recipes see cyanotype toning, and for cloth see cyanotype on fabric.

Note: Toning involves bleaching the image first; if you don't like the result, you cannot recover the original.

Troubleshooting

New Cyanotype (Mike Ware)

Developed by Dr. Mike Ware in the 1990s, the New Cyanotype addresses several shortcomings of the traditional process. It uses ferric ammonium oxalate instead of the citrate, producing faster printing, better tonal separation, and improved adhesion to paper.

Key Advantages

• Single solution (no mixing at time of use)
• Much faster exposure (about 2-4 minutes under an average UV source, against 30 minutes or more for the traditional sensitiser, per Ware)
• Better tonal range and Dmax
• Improved paper adhesion
• No tackiness problems with negatives

New Cyanotype Sensitiser

Preparation (Ware): Dissolve the potassium ferricyanide in 20 ml of distilled water at about 70 °C and keep it hot. Dissolve the ammonium ferric oxalate in 30 ml of distilled water at about 50 °C, then dissolve the ammonium dichromate in the oxalate solution. Add the hot ferricyanide solution to the oxalate solution, stir, and leave in the dark for one to two hours to cool. Green crystals of potassium ferric oxalate (about 15 g) separate out. Filter them off and discard them safely, then make the filtrate up to 100 ml with distilled water. Filter again and store in a brown bottle in the dark. Do not skip the crystallisation and filtering step: without it the sensitiser is gritty and crystallises on the paper.

Note: The sensitiser contains oxalates and is harmful if swallowed or in contact with skin. Ammonium dichromate warning: ammonium dichromate is classed as a Category 1B carcinogen, mutagen and reproductive toxin, fatal if inhaled, toxic if swallowed, corrosive, and a skin and respiratory sensitiser (signal word Danger). It is on the REACH Authorisation List (Annex XIV, retained under UK REACH), so it is hard to buy. If you use it, buy it as a ready-made dilute solution rather than as powder, wear nitrile gloves and eye protection, never handle the dry powder without dust control, and dispose of it as hazardous waste.

Paper Selection

Recommended Papers

• Arches Platine: Industry standard, works excellently
• Hahnemühle Platinum Rag: Specifically formulated for iron processes
• Bergger COT320: Heavy cotton rag, excellent results
• Stonehenge: Affordable option that works well
• Fabriano Artistico: Good general-purpose watercolour paper

Avoid papers with alkaline buffers (most "archival" papers marked acid-free), as these can inhibit the iron chemistry.

Safety

Traditional cyanotype is one of the safest alternative processes and is suitable for educational settings with appropriate supervision.

Further Reading

Mike Ware, Cyanotype: The History, Science and Art of Photographic Printing in Prussian Blue (Science Museum/NMSI, 1999) The first published monograph on cyanotype. Now out of print; Ware's later e-book Cyanomicon (2014) updates it and is offered on mikeware.co.uk. Covers history, chemistry, conservation, and practice.

Christina Z. Anderson, Cyanotype: The Blueprint in Contemporary Practice (Routledge, 2019) Part of the Contemporary Practices series. Over 100 papers tested, 400 photographs from nearly 80 artists. Covers classic, new, and other cyanotype formulas plus toning and alternative surfaces.

Christina Z. Anderson, Cyanotype Toning (Routledge) Part of the Routledge Contemporary Practices series, dedicated entirely to toning methods for cyanotype.

Christopher James, The Book of Alternative Photographic Processes, 3rd Edition (Cengage Learning, 2015) The definitive comprehensive text on alternative processes, with extensive coverage of cyanotype alongside 27 other chapters.

Mike Ware's website (mikeware.co.uk) Primary source for the New Cyanotype formula, with free downloads of complete workshop notes and technical papers.

Sources

• Traditional Cyanotype, Mike Ware
• The New Cyanotype Process, Mike Ware
• Cyanotype Kit Instructions, Bostick & Sullivan
• Ammonium dichromate substance information, ECHA
• Supplying explosives precursors and poison substances: list of chemicals, Home Office (GOV.UK)