Historical Context
Oil printing was introduced by G.E.H. Rawlins in 1904 as a variant of the carbon process. It became the direct precursor to bromoil, which adapted the same principles to silver gelatin prints. During the Pictorialist era (1890s-1920s), oil printing was prized for its painterly qualities and the extensive control it offered photographers.
The process uses dichromated gelatin sensitised on paper, exposed to UV light, then inked by hand. The differential hardening of the gelatin allows ink to adhere to shadow areas while being repelled by the swollen, unhardened highlights.
Chemistry
Gelatin Sizing Solution
| Component | Amount |
|---|---|
| Photographic gelatin | 15 g |
| Distilled water | 300 ml |
Sensitiser
| Component | Amount |
|---|---|
| Potassium dichromate | 5 g |
| Distilled water | 100 ml |
Or use ammonium dichromate for slightly higher sensitivity.
Procedure
Paper Preparation
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Size the paper: Soak paper in warm gelatin solution (45°C) for 3 minutes. Hang to dry. Repeat 2-3 times for adequate gelatin layer.
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Sensitise: Float dried, sized paper on dichromate solution for 3 minutes. Hang to dry in darkness.
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Storage: Sensitised paper can be stored in a dark box for several days if kept dry.
Exposure
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Contact print: Place sensitised paper under negative in contact frame.
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Expose: Expose to UV light or strong sunlight. The image will appear in yellow-brown tones as the dichromate hardens the gelatin in the shadow areas.
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Judgment: Exposure is complete when a faint image is visible. Over-exposure hardens too much gelatin; under-exposure leaves too little.
Inking
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Wash out: Wash the exposed print in cool water (20°C) for 10-15 minutes. The unhardened gelatin in highlights swells while hardened shadow areas remain firm.
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Surface preparation: Blot excess water but keep paper damp.
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Apply ink: Using stiff brushes, stipple lithographic ink onto the damp print. The hardened shadow areas accept ink; the swollen highlight areas repel it.
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Build density: Work gradually with repeated applications. The image builds through successive inkings.
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Dry: Allow to dry completely between inking sessions if multiple applications needed.
Inks and Tools
Recommended Inks
- Lithographic printing inks (Charbonel, Graphic Chemical)
- Oil-based relief inks
- Custom mixtures with linseed oil for consistency control
Brushes
- Stiff hog bristle for stippling
- Badger blenders for smoothing
- Various sizes for different image areas
Comparison with Bromoil
| Aspect | Oil Printing | Bromoil |
|---|---|---|
| Starting point | Sized paper | Silver gelatin print |
| Sensitiser | Dichromate | Silver image (bleached) |
| Negative required | Yes (contact) | No (enlargement possible) |
| Hazard level | Higher (dichromate) | Lower (no dichromate) |
| Preparation | More steps | Simpler |
| Image quality | Potentially higher | Dependent on original print |
Troubleshooting
| Problem | Likely Cause | Solution |
|---|---|---|
| Ink won't adhere | Paper too wet; under-exposure | Blot more; increase exposure |
| Ink in highlights | Paper too dry; over-exposure | More water; reduce exposure |
| Uneven gelatin | Poor sizing technique | Multiple thin coats |
| Low Dmax | Insufficient inking | More ink; stiffer ink |
| Image washes off | Under-exposure; weak gelatin | Increase both |
Safety
| Chemical | Hazard | Precautions |
|---|---|---|
| Potassium dichromate | Carcinogenic (hexavalent chromium) | Gloves essential; excellent ventilation; avoid skin contact |
| Ammonium dichromate | Carcinogenic | Same as above |
| Gelatin | Non-toxic | Standard precautions |
| Lithographic ink | Skin irritant | Gloves; ventilation |
Oil printing uses dichromates which contain hexavalent chromium, a known carcinogen. This process requires proper safety equipment and ventilation. Consider bromoil as a safer alternative that produces similar results.
Gum Oil Variant
Some practitioners combine gum bichromate with oil printing:
- Print a gum bichromate layer first (for colour)
- Apply oil printing layer on top
- Results in multi-layer, multi-colour prints
This hybrid technique was popular among Pictorialists for achieving complex tonal and colour effects.
Further Reading
Bertram Cox, The Art of Photo Oil (self-published, 1920s) Historical reference from the process's peak period.
Luis Nadeau, History and Practice of Oil and Bromoil Printing (Atelier Luis Nadeau) Comprehensive modern reference covering both processes.
Robert Demachy and Constant Puyo's work Pictorialist masters who used oil printing extensively. Their prints demonstrate the process's artistic potential.