Ethanol

For fifty years photography ran on this liquid. Collodion is nitrocellulose dissolved in ether and alcohol; a gelatine emulsion was washed with it, drained with it, coated with the help of it and dried in it. Then the industry moved to water, and alcohol became a specialist’s reagent again.

In photography

Collodion. Hardwich’s 1864 manual devotes a chapter section to “the solution of the Pyroxyline in Ether and Alcohol”, and is exacting about which alcohol. Rectified spirit of wine at specific gravity 0.836, he writes, “is very suitable for adding to developing fluids, etc., but not sufficiently strong for good Collodion”; he settled on “a strong Alcohol obtained by one distillation”. The reason is contamination, not water: rectifiers economised by blending in “faints”, which “are invariably contaminated with essential Oils”, and Hardwich holds that in photography it is most important to avoid essential oils. A separate section covers the use of alcohol to retard the evaporation of collodion in hot climates. Mike Ware notes the plain consequence of all this: the wet-plate worker’s solvent was “diethyl ether mixed with ethanol”, and that presented a hazard.

Washing an emulsion, without water. Abney gives Wratten and Wainwright’s method: after the emulsion has rested two or three hours, pour in two ounces of alcohol for each ounce of water used and shake. “The gelatine rapidly assumes a pasty appearance, and subsides to the bottom”, and the liquid poured off carries the soluble nitrates away with the water. Methylated spirit serves if it contains no gum, “and the lower the specific gravity the more effectual it is”. The same trick fixes an over-wet emulsion at the draining stage.

⚗The chemistry

Abney states the mechanism in one clause: “the alcohol has a greater affinity for water than has the gelatine, and … in extracting the water the soluble salts are extracted with it.” Ethanol is miscible with water in all proportions and gelatin is not; put enough of it into a swollen gel and the water leaves the protein for the solvent, taking the dissolved nitrates with it, and the dehydrated gelatin collapses out as a paste. The same page records the limit of the effect — “alcohol and carbolic acid, in large quantities, precipitate gelatine from solution in water” — which is a warning as much as a technique: an emulsion shocked with too much alcohol is coagulated, not washed.

That single property covers three of the four uses on this page: washing is dehydration of the gel, rapid drying is dehydration of the finished film, hardening an albumen layer is dehydration of a protein. Only the fourth, dissolving pyroxylin and resins, is ethanol acting as an ordinary solvent.

Coating. Abney’s account of Bennett’s gelatino-bromide process adds three-quarters of an ounce of pure alcohol, warmed to 90 °F, to eight or nine ounces of melted emulsion before making it up to ten ounces and coating; beginners are told to double it. The mottling that appears “directly after coating … subsides in a few seconds to an even surface”, the extra alcohol “does not appear to alter the sensitiveness, and is a great help”, and its whole purpose is to be “sufficient to draw the emulsion up to the edges” — because “when no alcohol is used you always have thin edges, which is very objectionable, as the negative, of course, will print dark at those parts”. That is a wetting agent doing a wetting agent’s job, seventy years before Photo-Flo.

Drying. Wall’s 1912 Dictionary has an entry for it: negatives can be dried “within five minutes of leaving the washing water … by taking advantage of the property of methylated spirit to displace the water within the pores of the gelatine”. There is a right way to do it. The spirit must be strong, and because “the water extracted from each soon weakens the spirit”, a batch of negatives goes through three successive baths rather than one. A separate entry, “Drying by Alcohol”, gives ten minutes in methylated spirit free from resinous matter, after which a plate dries in an hour — with the flat warning that “modern methylated spirit is not suitable”, for reasons this page’s History section explains.

Properties

A clear colourless liquid with a weak vinous odour, boiling at 78 °C, freezing at −114 °C, relative density 0.79. Miscible with water in all proportions, and with ethyl ether, acetone, chloroform and most organic solvents — that double miscibility is what makes it a bridge between a resin and a wash bath.

The fire numbers: vapour pressure 5.8 kPa at 20 °C, flash point 12.0 °C, auto-ignition 400 °C, and explosive limits that Chemical Safety Card 0044 gives as 3.1 to 27.7 vol% in air while CAMEO gives 3.3 to 19. Either way the upper limit is high — a room with spilled alcohol in it stays flammable over a wide range of concentrations. CAMEO gives the vapour density as 1.59, heavier than air. The card’s summary is the same as for its neighbour on the shelf: “The vapour mixes well with air, forming explosive mixtures readily”, though harmful air contamination “develops rather slowly at 20 °C”.

Nineteenth-century sources measure alcohol by specific gravity, and Wall’s dictionary explains why: with nothing but water present, the strength “can be very rapidly and accurately determined … by taking the specific gravity”. A photographer with a hydrometer knew what was in the bottle, which is why Hardwich can specify 0.836 and expect to be understood.

Handling

The aggregated ECHA notifications classify ethanol Danger, with the flame and exclamation-mark pictograms. Of 13,881 classifying reports, more than 99.9 per cent give H225, highly flammable liquid and vapour; H319, serious eye irritation, appears in 37.7 per cent, which is a genuine split among a very large number of notifiers. Five reports out of 13,886 say it meets no criterion. HSE’s EH40 sets a workplace exposure limit of 1000 ppm (1920 mg/m³) over eight hours with no short-term limit listed; NIOSH and OSHA give the same 1000 ppm, and NIOSH’s IDLH of 3300 ppm is again set at 10 per cent of the lower explosive limit rather than on toxicity. Chemical Safety Card 0044 records severe eye irritation, irritation of the respiratory tract, possible effects on the central nervous system, and defatting of the skin on long-term contact.

Why Level B. This is a rubric decision rather than a toxicological one, and the page says so. The course rubric admits to Level A “no volatile organic solvents beyond isopropanol in small quantities” — it names one alcohol, and this is not it, so any procedure using ethanol as a solvent starts at Level B under the criteria covering vapours and burns. By the numbers the two alcohols are close: flash points 12.0 and 11.7 °C, densities both 0.79, and EH40’s limit for ethanol is less strict at 1000 ppm than propan-2-ol’s 400 ppm. What separates them is quantity and context. Isopropanol arrives as 70 per cent rubbing alcohol and is used by the tens of millilitres; the ethanol procedures on this page are collodion mixing, litre-scale washing baths and open dishes of spirit.

⚠Safety

Extraction or a through draught, no ignition source in the room or the extract path, the smallest working quantity, the bottle closed between pours. Goggles over an open dish; nitrile gloves; the skin effect is defatting rather than corrosion, but it is cumulative. Store it fireproof and cool. The incompatibility that matters most in a darkroom is on Chemical Safety Card 0044’s own list: ethanol “reacts violently with strong oxidants such as nitric acid, silver nitrate, mercuric nitrate and magnesium perchlorate”, and reacts slowly with silver oxide and with ammonia to generate a fire and explosion hazard. Silver nitrate, ammonia and alcohol are all present in a nineteenth-century printing room and in a modern emulsion bench. Keep them apart, and never store alcohol in the silver cupboard.

Waste

Kodak’s J-300 guidance rules solvents and flammable materials out of the sewer by name, and ethanol is both. Traces on cloths and swabs evaporate in open air away from any ignition source; unused liquid is bottled, labelled and taken to a household waste and recycling centre’s chemical cupboard — ILFORD’s route for domestic users in the United Kingdom — or to a licensed contractor. One stream here needs separating from the others: alcohol used to precipitate or wash an emulsion comes out carrying soluble silver salts as well as gelatin, so it is a silver-bearing waste and a flammable one and cannot be treated as either alone. Label it for what it is. Check your local regulations, which govern and which are strictest of all for flammable liquid.

History

The most photographically consequential thing that ever happened to ethanol was a tax rule. Wall’s 1912 Dictionary explains it. Methylated spirit — rectified spirit with 10 per cent crude wood spirit added to make it unpalatable — had long been sold free of the heavy duty on alcohol. Then “by a regulation which came into force in 1891 such methylated spirit as is sold retail in the shops must contain, in addition to the 10 per cent. of crude wood spirit,” a fraction of one per cent of petroleum of specific gravity not less than 0.800. The consequence was immediate and physical: “this petroleum is separated on the addition of water, rendering the liquid milky or turbid; and methylated spirit containing the petroleum is partially unfitted for several uses to which it was formerly applied in connection with photography.” A photographer who wanted the old spirit had to buy ten gallons at a time under a permit from the Excise Department at Somerset House, and be visited by a local exciseman first.

That is why Wall’s drying entry says flatly that modern methylated spirit is not suitable, and why the alcohol on a darkroom shelf after 1891 was either expensive, bureaucratic or wrong — a small reminder that photographic practice is shaped by revenue law as well as by chemistry.