Skip to main content

Alternative process

Gelatin Dry Plate

AdvancedHigh hazard
Hand-made silver gelatin dry plates: Terry Holsinger's neutral iodobromide emulsion formula, coating, exposure and development, with silver nitrate hazards.
Difficulty
Advanced
Hazard level
High
Category
Silver
Reading time
8 min

High hazard

Silver nitrate is oxidising and corrosive (H272, H314, H410) and stains skin permanently; potassium bromide H319. Gloves, eye protection, ventilation, safelight. Check supplier SDS for potassium iodide and developers.

At a glance

Image characteristics

Slow, blue-sensitive silver gelatin negatives on glass, with the look of 19th-century dry plates

Key chemicals

  • Silver nitrate
  • Potassium bromide
  • Potassium iodide
  • Gelatin

Historical context

Wikipedia's "Dry plate" article says the gelatin silver process is commonly attributed to Richard Leach Maddox, whose 1871 article described an experiment with gelatino-bromide. It credits Charles Harper Bennett with hardening the emulsion in 1873 (tagged "citation needed") and, in 1878, with showing that prolonged heating greatly increases its sensitivity, which helped make instantaneous photography common. George Eastman developed a plate-coating machine in 1879 and founded the Eastman Film and Dry Plate Company in 1881. The article cites few of these dates, so we give no single inventor or year.

Dry plates replaced wet collodion because they could be bought, stored and exposed days later, then developed at leisure.

What it is and how it differs

  • Silver halide in gelatin on glass. A gelatin emulsion of silver bromide and a little iodide is coated on a glass plate, set, dried and exposed in a camera. This is the same family as modern film, made by hand.
  • Dry, not wet. Unlike wet plate collodion, the plate is coated and dried in advance, and exposed and developed at any time.
  • Slow, blue-sensitive and variable. Terry Holsinger's workshop emulsion measured about ASA 5 and ASA 2 in two sessions, and the emulsion is blue-sensitive, so medium to light blues wash out (Holsinger).
  • Much harder than buying plates. Beginners can skip the chemistry with a commercial liquid emulsion; see liquid emulsion.

Materials and chemistry

Holsinger's neutral iodobromide emulsion is the only complete published formula we fetched. The workshop used the 14 g column. His 441 mL batch coated about 60 4x5 plates.

IngredientFor 28 g AgNO3For 14 g AgNO3
Bromide solution: potassium bromide23.1 g11.55 g
Bromide solution: potassium iodide0.7 g0.35 g
Bromide solution: gelatin9.1 g4.55 g
Bromide solution: distilled water238 mL119 mL
Silver solution: silver nitrate28 g14 g
Silver solution: distilled water280 mL140 mL
Extra gelatin, dry35 g17.5 g
Further gelatin14 g7 g
Water to a total of 6.3 kg882 mL441 mL

For a different recipe, follow the instructions of the publication you are using. Holsinger lists developers as Kodak D-8 (2:1), HC-110 (dilution A) or Dektol (1:1).

Equipment

Holsinger's sessions used a temperature-controlled water bath, a safelight for the silver step, a red LED for development by inspection, cheesecloth for the noodle wash, and a dropper, plastic spoon or glass rod for coating. Holsinger mentions an optional hardener added just before coating but gives no formula for it; follow the hardener's own instructions. He also found thicker coatings worked best.

Procedure

Holsinger's emulsion method, in outline. Follow his page for the full washing options.

  1. Clean the glass. Scrub both sides with powdered cleanser under running water, rinse with tap then distilled water, and dry in a rack. Sand sharp edges.
  2. Mix. Bring the halide solution to 70 °C in a water bath. Under safelight dissolve the silver nitrate in 70 °C water.
  3. Precipitate. Add the silver to the halide at 70 °C while stirring. Slow addition gives a faster emulsion, fast addition a slower one.
  4. Ripen. Hold at 70 °C for 20 minutes, then cool to 45 °C. Add the dry extra gelatin slowly and stir for another 20 minutes.
  5. Wash. The page describes two ways of removing by-products: ethanol leaching (a thin emulsion with little density) and chilling and "noodling" with cold distilled water (thicker, moderate density).
  6. After-ripen. Add the remaining gelatin and water, heat slowly to no more than 60 °C for no more than 30 minutes, then cool to 40 °C. Excess heat or time causes fog. Test a coated strip and stop when fog first appears.
  7. Coat. About 4 mL per 3x4 inch plate, poured on a level plate. Chill on a cold level surface for about ten minutes, then dry in the dark for hours.
  8. Expose. Start at 1/30 s at f/8 and adjust.
  9. Develop and fix. Develop by inspection for 4 to 12 minutes under a red LED, stop in water, fix for 4 to 15 minutes until the back of the plate is clear, then rinse for 5 minutes.

Troubleshooting

ProblemLikely causeRemedy
Coating lifts in processingCracked or chipped edges, uneven cleaning, thin picture-frame glassSand edges, clean consistently, use thicker glass (Holsinger)
Pink tintFixing not completeRe-fix; this helped once (Holsinger)
FogAfter-ripening too long or too hotStop at first sign of fog (Holsinger)
Thin, low-density emulsionEthanol washingTry the noodle wash (Holsinger)
Very slow platesNormal for this recipeExpect ASA 2 to 5 (Holsinger)

Safety

Warning

Silver nitrate is corrosive and oxidising, and stains skin and clothing permanently. Holsinger warns it can cause blindness: keep it out of your eyes and do not breathe the dust. Wear gloves, eye protection and an apron, and work in good ventilation. Heated ethanol vapour made most participants in Holsinger's first session feel "high", so ventilate or use a half-mask respirator.

ChemicalHazards
Silver nitrateDangerMay intensify fire; oxidiser.; Causes severe skin burns and eye damage.; Very toxic to aquatic life with long lasting effects.
Potassium bromideWarningCauses serious eye irritation.

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.

  • Silver nitrate is classed H272, H314 and H410 (harmonised CLP). Silver is toxic to aquatic life (H410), so do not pour spent solutions down the drain; ask your local waste service how to dispose of them.
  • Potassium bromide is classed H319 (the classification agreed by REACH registrants; no harmonised entry).
  • Potassium iodide is not in our chemicals database; read the supplier's data sheet.
  • Developers and fixers. Holsinger names the developers but no chemical details; read the SDS for the product you buy.
  • Glass. Sharp edges cut hands (Holsinger).
  • COSHH. Treat silver nitrate and the developers as hazardous substances: assess the risk before you start, especially if others use the space.
  • Not for beginners alone. Holsinger's page describes workshop sessions; learn the safe handling of silver nitrate from an experienced person if you can.
  • Storage. Keep silver nitrate in a labelled, closed container away from combustible materials, since it is an oxidiser (H272).

Further reading

Mark Osterman and Nick Brandreth wrote the emulsion-making manual used in the George Eastman Museum's gelatin dry plate workshops (workshop listing, 2016). It is handed out as part of a course, not published as a free text.

Terry Holsinger, "Dry Plate Workshop" on Unblinking Eye, the source of the formula above.

Sources

Primary reference

Terry Holsinger, Dry Plate Workshop v2 (Unblinking Eye)

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