Historical context
William Willis patented platinum printing in 1873 (British Patent 2011, 5 June 1873) and founded the Platinotype Company in 1879. That process was a develop-out one. In 1887 Giuseppe Pizzighelli and Hübl succeeded with a print-out platinum process, in which the image appears during exposure. Platinum printing peaked around 1900, was hit by the First World War, and the company was wound up in 1937 (Mike Ware, "The Eighth Metal"). A worldwide revival began in the mid-1970s.
The contemporary print-out method comes from Pradip Malde and Mike Ware, whose book Platinotype: Making Photographs in Platinum and Palladium with the Contemporary Printing-out Process (Routledge, 2020) is the definitive manual. Ware's free workshop notes, on which the chemistry below is based, describe a print-out method with an iron sensitiser derived from Pizzighelli's. We give no single inventor or year for the modern method.
What it is and how it differs
- Print-out, not develop-out. The image forms mainly during exposure, at about 50 to 80% relative humidity, with little or no development (Ware).
- Judged by eye. You inspect the printed-out image directly instead of making test strips.
- Self-masking. Shadows resist blocking up.
- Ammonium salts and EDTA clearing. The sensitiser uses ammonium iron(III) oxalate, platinum and palladium as ammonium chloro-salts. The wet processing is a sequence of EDTA baths and a reducing bath.
- No oxidising contrast agents. Ware warns that potassium chlorate, potassium dichromate and hydrogen peroxide truncate highlights instead of compressing tones evenly. Contrast is set by the platinum to palladium ratio and by humidity.
Traditional develop-out printing, by contrast, dries the paper thoroughly, needs test strips, and develops in hot concentrated potassium oxalate, which is toxic (Ware). Our platinum/palladium guide covers both approaches.
A note on "Na2": in the print-out method we found no sourced "Na2 contrast" step. Ware uses disodium EDTA (Na2EDTA) as the first clearing bath, not for contrast. We do not describe any other Na2 contrast method.
Materials and chemistry
Ware says GPR-grade chemicals are adequate. These are his stock solutions:
| Solution | Recipe | Notes |
|---|---|---|
| Iron (Fe), 60% w/v | 30 g ammonium iron(III) oxalate in 33 cc distilled water, warmed to about 50 °C; makes about 50 cc | Filter; store in a dark bottle |
| Platinum (Pt), 25% w/v | 5 g ammonium tetrachloroplatinate(II) in 18 cc water; makes about 20 cc | Stand at least 24 hours before first use; decomposes, so do not store large amounts |
| Palladium (Pd), 20% w/v | 5 g ammonium tetrachloropalladate(II) made up to 25 cc; or 1.8 g ammonium chloride in about 20 cc hot water, with 3 g palladium(II) chloride, kept hot for about an hour, made up to 25 cc and filtered |
Mixing
| Mix | Stand | |
|---|---|---|
| Platinum | Equal volumes Fe and Pt | One hour in the dark |
| Palladium | Equal volumes Fe and Pd | Coat immediately |
| Mixed | Any Pt:Pd ratio, Fe equal to Pt plus Pd | One hour in the dark |
About 0.3 to 0.4 cc sensitiser covers a 5x4 inch print, and 1.2 to 1.6 cc a 10x8. Mix at room temperature under tungsten light, using a separate syringe for each solution. Ware suggests starting with palladium alone, which is cheaper, more forgiving and works on more papers.
Procedure
- Choose the paper. For pure platinum, avoid gelatin size and calcium carbonate buffer, because gelatin binds platinum(II). Starch, Klucel G or Aquapel (AKD) sizes are compatible. Palladium is not inhibited by gelatin.
- Humidify. The best range is 50 to 80% RH. Below 50% you get partial print-out, more development and browner tones; above 80% maximum density weakens. A tank above a saturated salt solution gives a fixed humidity: ammonium chloride about 80% at 20 °C, calcium nitrate tetrahydrate about 55%. Allow at least half an hour.
- Coat with a glass rod, which Ware says uses under half the volume of brushing. Rest the paper horizontally until non-reflective under tungsten light.
- Dry for about ten minutes in warm air at 40 °C or an hour at room temperature in the dark. Check for surface crystals, which can damage negatives. Use within a few hours if possible.
- Expose in contact with the negative under strong UV. Typical times are a few minutes, with palladium about twice as fast as platinum. Keep going until the printed-out image looks right.
- Clear. Ware's sequence:
| Step | Bath | Time |
|---|---|---|
| 1 | Disodium EDTA, 5% w/v (pH about 3 to 4) | 10 minutes |
| 2 | Water rinse | Half a minute |
| 3 | Hypoclear working solution or sodium sulphite | 10 minutes |
| 4 | Water rinse | Half a minute |
| 5 | Tetrasodium EDTA, 5% w/v (pH about 9) | 10 minutes |
| 6 | Running water | At least 30 minutes |
Check the unexposed areas under bluish light: yellow stain means clearing was not adequate. The disodium bath has a capacity of about 50 10x8 inch prints per litre.
- Wash and dry. Wash about an hour, drain without touching the wet surface and dry face up. Retouch with permanent watercolour.
Contrast and colour
| Sensitiser | RH | Colour (Ware) |
|---|---|---|
| Platinum | 32% and 55% | Warm black |
| Platinum | 80% | Neutral |
| Palladium | 32% | Sepia |
| Palladium | 55% | Van Dyke brown |
| Palladium | 80% | Warm black |
| Pt:Pd 3:1 | 32% | Warm black |
| Pt:Pd 3:1 | 55% and 80% | Neutral |
Ware notes a 3:1 platinum to palladium mix gives fairly constant contrast and speed across 40 to 70% UK ambient humidity. Values vary with paper.
Troubleshooting
| Problem | Likely cause | Remedy |
|---|---|---|
| Yellow stain in whites | Clearing inadequate | Check every bath and time in the sequence was followed (Ware) |
| Weak density | Humidity above 80% or over-long humidifying | Reduce RH or humidifying time (Ware) |
| Brown, partly developed look | Humidity below 50% | Humidify the paper before coating (Ware) |
| Pure platinum is poor | Gelatin size or buffered paper | Switch to starch, Klucel or Aquapel sizing (Ware) |
| Damaged negative | Surface crystals on the coating | Inspect for crystals before exposing; a protective polyester film is optional (Ware) |
Safety
Platinum chloro-complexes can cause asthma and dermatitis, and sensitisation can develop (Ware). Wear gloves, avoid touching sensitised paper, keep fingers out of the baths, ventilate well, and take care with dry powders. Ammonium iron(III) oxalate is harmful if swallowed or in contact with skin. Shield your eyes from the UV lamp.
| Chemical | Hazards |
|---|---|
| Ammonium iron(III) oxalate trihydrateWarning | Harmful in contact with skin.; Harmful if swallowed. |
| Potassium chloroplatiniteDanger | Toxic if swallowed.; Causes skin irritation.; Causes serious eye damage.; May cause allergy or asthma symptoms or breathing difficulties if inhaled.; May cause an allergic skin reaction. |
| Sodium chloropalladiteDanger | May be corrosive to metals.; Harmful if swallowed.; Causes serious eye damage.; May cause an allergic skin reaction.; Very toxic to aquatic life with long lasting effects. |
| Disodium EDTAWarning | Harmful if inhaled.; May cause damage to organs through prolonged or repeated exposure. |
| EDTA (edetic acid)Warning | Causes serious eye irritation. |
| Sodium sulfite (anhydrous) | Not classified as hazardous |
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.
- Platinum and palladium salts. The database holds potassium tetrachloroplatinate (H301, H315, H318, H334, H317) and sodium tetrachloropalladate (H302, H318, H317, H410), related compounds rather than Ware's ammonium salts. Check the supplier's data sheet for the exact salts. Ware describes palladium compounds as moderately toxic, with dust the main risk, and recommends them for people with a platinum allergy.
- Ammonium iron(III) oxalate is classed H302 and H312. Ware calls it highly toxic if swallowed, mainly a kidney risk.
- EDTA. Ware calls the EDTA baths non-toxic compared with traditional clearing chemicals; the database's low-consensus entry for disodium EDTA lists H332 and H373, so wear gloves anyway.
- UV. Avoid lamps with significant UVB, which is harmful and can produce ozone (Ware).
- Save spent solutions for precious-metal recovery.
Further reading
Pradip Malde and Mike Ware, Platinotype (Routledge, 2020). Covers formulae, workflow summary sheets, paper chemistry, humidity control, troubleshooting and conservation advice, with work by more than 40 artists.
Mike Ware, Platinomicon. Free from mikeware.co.uk; a technical history of platinum and palladium printing.
Sources
- The Platino-Palladiotype Process, Mike Ware
- Platino-palladiotype workshop notes, Mike Ware (2009)
- The Eighth Metal, Mike Ware
- Platinotype by Pradip Malde with Mike Ware, Bostick & Sullivan (book listing)
- ECHA CHEM substance record: Ammonium iron(III) oxalate, European Chemicals Agency (hazard classification, via the Silverlog chemicals database)
- ECHA CHEM substance record: Potassium tetrachloroplatinate, European Chemicals Agency (hazard classification, via the Silverlog chemicals database)
- ECHA CHEM substance record: Sodium tetrachloropalladate, European Chemicals Agency (hazard classification, via the Silverlog chemicals database)
- ECHA CHEM substance record: Disodium EDTA, European Chemicals Agency (hazard classification, via the Silverlog chemicals database)