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Alternative process

Photogravure (Copper and Photopolymer)

AdvancedHigh hazard
Photographic intaglio printing: copper plate photogravure with dichromated gelatin tissue and ferric chloride, and photopolymer gravure with water-developed plates.
Difficulty
Advanced
Hazard level
High
Category
Colloid
Reading time
9 min

High hazard

Potassium dichromate is carcinogenic, mutagenic and reprotoxic (H350, H340, H360FD) and a sensitiser; ferric chloride causes serious eye damage (H318) and is harmful if swallowed; sodium hydroxide is corrosive (H314). Photopolymer route avoids dichromate and etchant.

At a glance

Image characteristics

Deep, velvety continuous-tone intaglio prints on damp paper with a fine grain

Key chemicals

  • Potassium dichromate
  • Ferric chloride
  • Sodium hydroxide
  • Gelatin

Historical context

Photogravure turns a photograph into an intaglio (etched) printing plate. Wikipedia says Henry Fox Talbot patented "photographic engraving" in 1852 and "photoglyphic engraving" in 1858, and that the mature form was developed in 1878 by the Czech painter Karel Klíč. Lloyd Godman's page instead dates Klíč's invention to 1879 and gives his lifespan as 1841 to 1926. Because sources differ, we credit no single inventor or year. In both accounts, Talbot's work came first and Klíč built on it. Photopolymer plates, such as the steel-backed Toyobo Printight KM73, arrived much later and give a similar result without gelatin tissue.

What it is and how it differs

This guide covers two ways of making the plate. The printing is the same for both: ink is pressed into the plate, wiped from the surface and printed on damp paper under an etching press.

  • Copper plate photogravure. A pigmented gelatin tissue is sensitised with potassium dichromate, exposed to a continuous-tone positive, laid down on a grained copper plate, developed in warm water and etched in ferric chloride. The gelatin hardens where light falls, so thin gelatin (the shadows) etches first (Krut; Godman).
  • Photopolymer gravure. A steel-backed light-sensitive polymer plate is exposed through a positive and developed in water. It uses no dichromate and no etchant. Wikipedia notes mixed reviews and says polymer plates lack the depth variation of copper.
  • A third, simplified route. Andrea Canducci's AlternativePhotography.com article adapts printed-circuit photoresist board: a high-contrast line image, a caustic soda developer and ferric chloride. It gives no half-tones and is marked "advanced users only".

Photogravure is advanced. The copper method needs controlled humidity and temperature, dichromate, a hot-water laydown and a press. Neither method is a casual home project.

Materials and chemistry

Copper plate

ItemDetailSource
SensitiserCold 4% potassium dichromate for a timed soakKrut (Kentridge studio)
Sensitiser (alternative)3.5% potassium dichromate for 3 minutesWikipedia
GrainFine stochastic or hard-dot mezzotint screen exposed separately, or aquatint grain (asphaltum or rosin) fused to the plateWikipedia; Krut
EtchantFerric chloride in 4 to 5 baths, strongest to weakestKrut
Etchant (circuit-board shortcut)Ferric chloride at about 250 g per litre of water, following the supplier's instructions; heating speeds etchingCanducci
Clean-upCaustic soda and chalk powder to remove ferric oxideKrut

We found no published Baumé values or bath schedule that we could fetch. David Morrish and Marlene MacCallum's book Copper Plate Photogravure lists chapters on preparing the ferric chloride and etching, with a Baumé appendix; use it for numbers.

Photopolymer plates

Toyobo KM73 is 0.73 mm thick and steel-backed (Boxcar Press). Takach Press describes the KM family as developed in lukewarm tap water, usually exposed in a multi-spectrum metal halide unit, calibrated with a Stouffer 21-step scale until a solid 14/15 is reached. We found no official exposure times. Follow your plate supplier's instructions.

Procedure

Copper plate (Krut's account of a studio workflow)

  1. Make a positive. Print a continuous-tone positive on transparent film.
  2. Prepare the room. The studio is kept near 60% relative humidity and 21 °C. Pigmented tissue is stored in the fridge.
  3. Sensitise the tissue in cold 4% potassium dichromate, squeegee it face down on clean plexiglass and dry it (about 90 minutes).
  4. Expose. Expose the aquatint screen first so light reaches the whole gelatin surface, then the positive.
  5. Lay down. Soak the exposed tissue in diluted isopropyl alcohol, squeegee it face down on copper and leave it against the plate for about 20 minutes.
  6. Develop the plate in water at 45 °C for about 2 minutes, peel the backing, then set the gelatin in cold water.
  7. Dehydrate and rest. Displace the water in the gelatin with isopropyl alcohol, dry at once with a hairdryer and leave for 24 hours in the studio conditions. Moisture left in the gelatin causes mottled marks that will etch.
  8. Etch through 4 to 5 ferric chloride baths, strongest first, then strip the gelatin and clean with caustic soda and chalk.
  9. Proof and print. Proof, correct, and print with intaglio ink on damp paper.

Photopolymer plate

  1. Expose the plate to a random-dot aquatint screen, then to the positive transparency (Wikipedia).
  2. Develop in lukewarm water (Takach). Exposure and washout vary with lamp and water temperature, so run test strips on scrap plate.
  3. Ink and print as for any intaglio plate.

Troubleshooting

ProblemLikely causeRemedy
Mottled marks that etchMoisture left in the gelatinDehydrate in alcohol, dry at once, rest 24 hours (Krut)
Highlights tarnishedCopper oxidationMetal polish removes tarnish and can open tones (Krut)
Plate wears quicklyCopper is softSteel-face the plate by electroplating (Krut)
Weak result on circuit-board plateUnder-developed or under-etchedRepeat the developing and etching steps (Canducci)
No aquatint texture on polymerExposure or washout wrongCalibrate with a step wedge on scrap plate (Takach)

Safety

Warning

Both copper methods use corrosive and toxic chemicals. Potassium dichromate is a carcinogen, mutagen and reproductive toxin (H350, H340, H360FD), toxic if swallowed or inhaled and a skin and respiratory sensitiser. Ferric chloride causes serious eye damage and is harmful if swallowed. Wear gloves, eye protection and a respirator for powders, ventilate well, and never wash dichromate or etchant down the drain.

ChemicalHazards
Potassium dichromateDangerMay intensify fire; oxidiser.; May cause cancer.; May cause genetic defects.; May damage fertility. May damage the unborn child.; Fatal if inhaled.; Harmful in contact with skin.; Toxic if swallowed.; Causes damage to organs through prolonged or repeated exposure.; Causes severe skin burns and eye damage.; May cause allergy or asthma symptoms or breathing difficulties if inhaled.; May cause an allergic skin reaction.; Very toxic to aquatic life with long lasting effects.
Sodium hydroxideDangerCauses severe skin burns and eye damage.
Iron(III) chlorideDangerMay be corrosive to metals.; Harmful if swallowed.; Causes skin irritation.; Causes serious 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.

  • Ferric chloride is in our chemicals database with the classification agreed by REACH registrants for the substance itself (H290, H302, H315, H318); most notifications to ECHA are stricter (H302, H314). The etchant is a solution, and two supplier safety data sheets differ by strength: a 10% Fe solution is H302, H315, H318 (with H290 on the ingredient), and a 20% solution lists H290, H302, H314, H315, H318 and H412. Check your supplier's SDS. Both recommend gloves and eye or face protection.
  • Dichromate use in the EU needs authorisation under REACH Annex XIV, and UK REACH retained it. If that is a barrier, the photopolymer route avoids it.
  • Sodium hydroxide is H314 (causes severe skin burns). It is a reportable poison under the UK Poisons Act at 12% w/w caustic alkalinity.
  • Isopropyl alcohol is used for laydown and dehydration; we did not fetch its SDS, so read the one from your supplier.
  • Photopolymer needs only water, according to Takach, but UV exposure still needs eye protection.

Further reading

David Morrish and Marlene MacCallum, Copper Plate Photogravure: Demystifying the Process. The fullest account of ferric chloride preparation and the Baumé etching sequence.

Dianne Longley, Printmaking with Photopolymer Plates. Recommended by Takach Press for photopolymer work.

Sources

Primary reference

David Krut Projects photogravure step-by-step; Wikipedia Photogravure; Takach and Boxcar photopolymer plate pages

This guide combines established practice with community experience. Always follow safety precautions and cross-reference with primary sources before mixing chemicals.