Historical context
Liquid emulsion is light-sensitive silver gelatin sold as a gel that you melt and brush, pour or dip onto a surface of your choice. It is the same family of material as the coating on darkroom paper, so it is exposed, developed and fixed with ordinary black-and-white chemistry. The manufacturers describe supports including wood, textile, glass, china, ceramics, metal, leather, stone and plaster. We have not found a source for who first sold a liquid emulsion, so this guide does not name an inventor or a year.
What it is and how it differs
- The emulsion is much slower than enlarging paper, so you expose it under an enlarger or other bright source, using test strips.
- Unlike a ready-made print, you are responsible for the support: it must be clean, and some materials need a barrier coat or a gelatin subbing layer.
- It is a darkroom process throughout: melting, coating and drying all happen under safelight.
- The result is a silver gelatin image on an object, so it can be a flat print, a tile, a stone or a piece of fabric.
Materials and chemistry
Two manufacturer systems are covered here. Always follow the instructions packed with your own emulsion, since formulations and batches change.
| Item | Foma emulsion (1 kg) | Rollei Black Magic |
|---|---|---|
| Melting | About 35 to 40 °C in a water bath | Warm to about 40 °C in a bath at 40 to 45 °C |
| Hardener | 15 ml of supplied hardener per 1 kg, added to the melted emulsion | RBM5 additive hardener, formaldehyde-free; use the emulsion within 2 hours once added |
| Layers | A single layer on horizontal surfaces; 2 to 3 layers by brush, each after the last has dried | Several thin coats on 3-D objects |
| Storage | 4 to 10 °C, in darkness, do not freeze | Refrigerator, 6 to 8 °C |
| Shelf life | About 6 months for the emulsion without hardener | One year if stored as directed |
| Yield | 3 to 6 sq. m per kg; plan on about 3 sq. m for hand-brushed layers | Up to 8 m² non-absorbent, 4 m² absorbent |
Do not re-chill melted emulsion that contains hardener. Take only what you need from the stock.
Preparing the support
- Clean everything of dust and grease. Rollei warns that any trace of grease causes adhesion problems.
- Absorbent supports (fabric, paper, wood): Rollei recommends a precoat of its pure photographic gelatin, 40 g per litre of distilled water at 70 to 80 °C for non-absorbent surfaces and 80 g per litre for card or fabric.
- Metal, plastic, glass and ceramic tiles: Rollei says to precoat with alkyd resin primer or oil-based polyurethane. On metal an insulating layer is also needed to avoid an electrochemical reaction with the silver emulsion.
- Foma gives a gelatin subbing recipe that relies on a chromium hardener. We have not reproduced it because we hold no hazard source for that substance. Use the manufacturer's supplied hardener and, for difficult surfaces, follow the kit or reference instructions.
Safety
Read the safety data sheet for your emulsion before you start. Rollei states that its emulsion contains 0.1% phenol as a preservative. Wear gloves, work in a ventilated room, and if you spray, use a spray gun with a wide jet and wear protective clothing and a mask, as Rollei advises. Foma says that other hardeners such as formaldehyde can be used; we do not recommend that route, because formaldehyde may cause cancer (H350) and is fatal if inhaled (H330) under its CLP classification, and it is a UK reportable poison at 5% w/w.
| Chemical | Hazards |
|---|---|
| FormaldehydeDanger | May cause cancer.; Suspected of causing genetic defects.; Fatal if inhaled.; Harmful if swallowed.; Causes severe skin burns and eye damage.; May cause an allergic skin reaction.; Corrosive to the respiratory tract. |
| HydroquinoneDanger | Suspected of causing cancer.; Suspected of causing genetic defects.; Harmful if swallowed.; Causes serious eye damage.; May cause an allergic skin reaction.; Very toxic to aquatic life. |
| Acetic acidDanger | Flammable liquid and vapour.; Causes severe skin burns and eye damage. |
| Sodium thiosulfate pentahydrate | 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.
Many paper developers contain hydroquinone, so its classification is shown here; check your own developer's data sheet. Treat the fixer and the first washes as silver-bearing waste and ask your local environmental protection officer how to dispose of them, as Rollei advises. Do not use cooking utensils for chemistry, as Ilford notes.
Rollei processing solutions
Rollei publishes these working dilutions for its own chemistry; the stop bath and fixer figures are the clearest in its manual.
| Step | Product | Working dilution |
|---|---|---|
| Stop bath | RCS citric stop | 1+19 (50 ml in 950 ml water at 20 °C) |
| Fixer | RXN pH-neutral fixer | 1+4 (200 ml in 800 ml water) |
| Wetting agent | RWA | 1+100 (1 ml in 999 ml distilled water) |
| Developer | RPN, with RBM5 hardener | Follow the manual; its printed quantities are hard to read, so check your copy |
Procedure
- Prepare the support. Clean it and apply any barrier or gelatin coat described above, in normal light. Let it dry.
- Check the safelight. Rollei recommends a dark red safelight for its emulsion and a fogging test before coating large areas. Foma says to use the safelight recommended for its fixed-contrast papers.
- Melt and coat. Warm the emulsion in a water bath, stirring gently to avoid bubbles. Foma suggests cooling to 30 °C before pouring onto horizontal surfaces. Coat test strips of paper at the same time.
- Set and dry. Rollei: setting takes about 1 to 2 hours, then dry in the dark for several hours up to a day, or with a hair dryer on a low heat that you have checked in the dark first.
- Expose with an enlarger, stopped down for 3-D objects. Make test strips first. Rollei's variable-contrast emulsion takes the usual contrast filters.
- Develop. Foma recommends an energetic developer because the layer is thick and silver-rich (it names Fomatol LQN and Fomatol P). Rollei suggests keeping solutions at 20 °C or below.
- Stop, fix and wash. Rollei's stop bath is diluted 1+19 and its fixer 1+4; do not use a fixer with hardener. Foma stresses perfect fixing and long washing, ideally in running water, or the image will not last.
- Dry flat or hung, away from light until fixed.
Variations
- Contrast. Rollei's variable-contrast emulsion (RBM3) responds to filters like variable-contrast paper: yellow for softer, magenta for harder. Its graded emulsion (RBM2) can be mixed in any ratio to get in-between grades.
- Tone. Rollei says water-soluble photographic dyes added to the gelatin precoat tint the image; a few drops usually suffice.
- Too dense. Rollei suggests bleaching an over-exposed image back with its sepia bleach (part A, 1+30). Check the data sheet for that product before use.
- Protection. Rollei suggests protecting finished objects with a clear polyurethane coat. Mechanical damage is the main enemy even after hardening.
- Cylinders and bottles. Rollei suggests a litho-film negative taped round the object and turned evenly under the enlarger for an even exposure.
Troubleshooting
| Problem | Likely cause | Remedy (Rollei) |
|---|---|---|
| Bubbles in the print | Heavy stirring or shaking | Stir slowly; add 10 to 20 ml of grain alcohol per 500 ml of emulsion |
| Uneven coating | Surface not level while setting | Level the object; apply several layers |
| Emulsion lifts in processing | Grease or anti-adhesion agents on the surface | Clean thoroughly or precoat with alkyd resin primer |
| Yellow cast | Too much additive hardener | Use less hardener |
Practical notes
- Start on a flat, smooth, absorbent surface such as watercolour paper before trying glass or stone; Rollei also advises practising on easy surfaces first.
- Use a wide natural-hair brush, 5 to 10 cm, as Rollei recommends,.
- Process large or heavy objects by pouring chemistry on from a measuring jug, working from bottom to top, as Rollei describes.
- Foma says only a thin film of emulsion needs to be spread for most smooth surfaces, because of its high covering power.
- Keep notes of layers, exposure and development for every object; results vary with surface and humidity.
Further reading
Christopher James, The Book of Alternative Photographic Processes covers hand-coated emulsions in the wider context of alternative processes. We have not cross-checked its formulas for this guide.
Sources
- Rollei Black Magic liquid photo emulsion instruction manual (R011901), Maco Photo Products
- Foma photographic emulsion: processing of B/W photomaterials (FEG25), Foma Bohemia
- Making your first black and white print, Ilford Photo
- Formaldehyde substance information, ECHA
- Hydroquinone substance information, ECHA