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Alternative process

Ambrotype

AdvancedHigh hazard
A collodion positive on glass: an underexposed wet plate negative that reads as a positive when backed with something dark.
Difficulty
Advanced
Hazard level
High
Category
Colloid
Reading time
8 min

High hazard

Ether and collodion are extremely flammable, with heavy vapour that can reach a distant flame. Silver nitrate is corrosive and nitric acid fumes are irritating; the bromo-iodizer contains cadmium bromide, a poison. Use a thiosulfate fixer; never potassium cyanide, which is fatal by any route. Glass plates also break.

At a glance

Image characteristics

Fine detail with milky-white highlights; positive appearance depends on the dark backing; fragile glass support

Key chemicals

  • Collodion
  • Ether
  • Silver nitrate
  • Ferrous sulfate
  • Ammonium thiosulfate

Historical context

An ambrotype is a wet collodion image on glass that looks positive because it is backed with something dark. The sources we read disagree on credit, so we give no single inventor or year. The Graphics Atlas names Frederick Scott Archer as the introducer of collodion wet-plate negatives in England in the late 1840s, and says Louis-Désiré Blanquart-Evrard noticed in 1850 that a slightly underexposed glass negative can look positive against a dark ground. It credits James Ambrose Cutting with a method, in 1854, of sealing two pieces of glass with Canada balsam, with the name suggested by Marcus A. Root. The Science and Media Museum puts the first collodion positive at around 1853 and notes that "ambrotype" strictly means Cutting's patented balsam-sealed variant, mostly found in America. Both agree the name is often used loosely.

Common use ran from about 1854 to 1865 (Graphics Atlas). High street studios had largely dropped it by the 1860s, though itinerant open-air photographers kept using it into the 1880s (Science and Media Museum). In England it was called a collodion positive; in the United States an amphitype.

What it is and how it differs

  • Underexposed negative on glass. Highlights are heavy silver deposits; shadows carry little or no silver. A dark backing shows through the shadows, so the picture reads as a positive.
  • Backing options. Paint or lacquer on either side of the glass, black velvet, fabric, paper, a tintype plate, or dark (for example red) glass, which needs no separate backing.
  • Backing position matters. Paint on the image side gives a correctly oriented picture; paint on the other side gives a laterally reversed one, like a daguerreotype (Graphics Atlas).
  • Fragile. Unlike a tintype, glass breaks and the plates were usually cased with a mat, cover glass and frame.

For the overview of the whole family, see wet plate collodion.

Materials and chemistry

The chemistry is the same as for the tintype, with a few glass-specific steps. Quantities below are from Bostick & Sullivan's kit instructions; for anything else follow the kit or reference instructions.

ItemBostick & Sullivan
Salted collodionCollodion and bromo-iodizer, 25 ml to 40 ml (or 50:80, 125:200, 250:400)
Glass adhesionAdd 3 to 5 ml of amino silane subbing per 100 ml of salted collodion
Silver bath10% silver nitrate, specific gravity 1.08, 16 drops of 7% nitric acid per 1000 ml
Developer1 part developer to 3 parts water, 20 to 30 seconds
Fixer250 ml rapid fixer to 750 ml water, 4 to 5 minutes, then wash 5 to 7 minutes

Cleaning the glass

Bostick & Sullivan: sprinkle a teaspoon of calcium carbonate on an 8x10-inch plate with a teaspoon of rubbing alcohol and rub both sides for about 30 seconds. Rinse with hot soapy water, then cool water until streak-free. Dry with paper towel, clean the emulsion side with a little rubbing alcohol, buff dry and dust with a static-free brush. Clean glass helps adhesion.

Procedure

  1. Clean the glass as above.
  2. Pour the collodion in room light, away from any flame. Rock it across the plate, drain the excess back into the bottle and let the solvents evaporate (30 seconds for 4x5 inches, 45 for 5x7, 60 for 8x10).
  3. Sensitise in the silver bath. Lower the plate in quickly to avoid hesitation lines, cover the tank or turn off the lights (yellow and red safelights are fine), and sensitise for 3 to 5 minutes. Drain from one corner for 30 to 45 seconds and wipe the back (Bostick & Sullivan).
  4. Expose while wet. Bostick & Sullivan's general figure is 1 to 2 seconds in bright sunlight at f/8 or f/11, depending on the subject; exposures vary greatly. Test, and aim for a thin negative: an ambrotype is an underexposed negative.
  5. Develop at 1+3 for 20 to 30 seconds, longer to pull up shadow detail.
  6. Fix and wash.
  7. Varnish and back. Varnish as for tintypes (warm plate, pour away from the flame, bake until wisps of smoke, allow a week to harden). Then add the backing of your choice.

Glass negatives from the same kit differ: dilute the developer 1+5, overexpose by 3 stops (8 times normal exposure), develop for 2 minutes in a tray and agitate every 15 seconds (Bostick & Sullivan).

Recognising an antique ambrotype

The Graphics Atlas lists these clues: a cased object with a glass support, milky-white highlights, and usually a studio or itinerant portrait with a cover glass, mat and preserver frame inside a protective case. They are often mistaken for daguerreotypes or tintypes. The Science and Media Museum adds that the backing was a black velvet pad in a presentation case, or a coat of black varnish in cheaper studios and seaside booths.

Choosing a backing

BackingNotes (sources)
Black velvet pad in a caseThe classic presentation (Science and Media Museum)
Black varnishCheaper studios and holiday booths (Science and Media Museum)
Paint or lacquerEither side of the glass (Graphics Atlas)
Fabric, paper or a tintype plateListed by Graphics Atlas
Dark or red glassNeeds no separate backing (Graphics Atlas)

Trying a backing on a dry, varnished plate before committing costs nothing and shows how much shadow density your exposure left.

Troubleshooting

ProblemLikely causeRemedy
Collodion lifts or slides offDirty or unsubbed glassClean thoroughly; add amino silane subbing (Bostick & Sullivan)
Comets and streaksParticles in the silver bathFilter the bath through a coffee filter
FogBath contaminationCorrect the pH; sun or boil the bath
Image reversed left to rightBacking on the wrong sidePaint on the image side for a correctly oriented picture (Graphics Atlas)

Safety

Warning

Wet plate work involves extremely flammable ether and collodion, corrosive and oxidising silver nitrate, and nitric acid. Work in a well-ventilated space with no flame or pilot light nearby, and wear eye protection, gloves and an apron. Never use potassium cyanide as a fixer: it is fatal by every route and releases hydrogen cyanide with acid. A thiosulfate fixer works well. Broken glass plates also cut: wear gloves when cleaning and handling them.

ChemicalHazards
Diethyl etherDangerExtremely flammable liquid and vapour.; Harmful if swallowed.; May cause drowsiness or dizziness.; May form explosive peroxides.; Repeated exposure may cause skin dryness or cracking.
Silver nitrateDangerMay intensify fire; oxidiser.; Causes severe skin burns and eye damage.; Very toxic to aquatic life with long lasting effects.
Nitric acidDangerMay intensify fire; oxidiser.; Fatal if inhaled.; Causes severe skin burns and eye damage.; Corrosive to the respiratory tract.
Acetic acidDangerFlammable liquid and vapour.; Causes severe skin burns and eye damage.
Ammonium thiosulfateNot classified as hazardous
Potassium cyanideDangerFatal if inhaled.; Fatal in contact with skin.; Fatal if swallowed.; Very toxic to aquatic life.; Very toxic to aquatic life with long lasting effects.; Contact with acids liberates very toxic gas.
Cadmium bromideWarningHarmful if inhaled.; Harmful in contact with skin.; Harmful if swallowed.; Very toxic to aquatic life.; Very toxic to aquatic life with long lasting effects.

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.

  • Ether and collodion are extremely flammable (ether flash point -45 °C; vapour about 2.6 times as dense as air; can form explosive peroxides; repeated skin contact dries and cracks the skin). Bostick & Sullivan warn their collodion boils at 35 °C (95 °F) and say not to store it near a water heater or pilot light. Source: ICSC 0355.
  • Cadmium bromide in the bromo-iodizer is harmful if swallowed, inhaled or in contact with skin and very toxic to aquatic life under its EU harmonised classification (ECHA). NOAA CAMEO Chemicals lists it as a poison (UN 2570); ingestion can cause kidney and liver injury. The harmonised entry does not classify it as a carcinogen, though a few notifiers do.
  • Nitric acid fumes are extremely irritating and corrosive to the respiratory tract; Bostick & Sullivan recommend a respirator. Above 3% w/w it is a regulated explosives precursor in the UK.
  • Sandarac varnish is highly flammable. Keep the wet varnish out of the flame.
  • Beginners should work under the supervision of an experienced wet plate photographer, and should ask the local waste authority how to dispose of spent chemistry.

Further reading

Quinn Jacobson, Chemical Pictures: The Wet Plate Collodion Book: Making Ambrotypes, Tintypes & Alumitypes. The standard modern reference.

Christopher James, The Book of Alternative Photographic Processes. Covers wet plate alongside other historical processes.

Sources

Primary reference

Quinn Jacobson, "Chemical Pictures: The Wet Plate Collodion Book"; Bostick & Sullivan kit instructions

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