Diethyl ether

This is a study entry. Diethyl ether is here because collodion is a solution and because you cannot understand the wet plate without understanding what it was dissolved in. The page gives the chemistry, the hazard data and the historical role, and gives no quantity, no ratio, no pour and no apparatus, because the course classifies collodion work at Level D and a Level D page is not a procedure.

In photography

It is one half of a solvent pair, and the pair is not optional. The AIC conservation wiki defines collodion as pyroxylin dissolved in alcohol and ether. Archer, writing in 1854 about his own process, records why both are needed: gun-cotton is not soluble in pure ether — that is, ether free from alcohol — a fact that caused real confusion at the time, because the early accounts said ether and the early experimenters using dry ether could not reproduce them. Ethanol is not a diluent here; it is a co-solvent without which the polymer stays in the jar.

The two solvents also do different physical jobs. Ether is the volatile one: it leaves fast, and its leaving is what turns a poured liquid into a film. Hardwich’s chapter on collodion has a section heading that says the whole thing — the use of alcohol to retard evaporation. The alcohol slows the ether down. Set a solvent that boils at 34 °C against one that boils at 78 °C and the mixture becomes adjustable: a plate that sets too fast is unworkable, and a plate that sets too slowly runs.

And the timing of that evaporation is the process. The AIC’s collodion page gives the mechanism: once the alcohol and ether have dried, the collodion becomes impervious to the processing solution. That is why the plate had to be sensitised, exposed and developed in one continuous run, and why photographers carried darkrooms into fields — the AIC puts the weight of the equipment and materials needed to make one negative at around 250 kilograms. The constraint that defines the whole workflow is a vapour pressure.

⚗Why a solvent this good is a hazard this large

The properties that make ether an excellent solvent for a nitrated polymer and the properties that make it dangerous are the same properties, and they cannot be separated by careful working.

It is very volatile. A vapour pressure of 440 mmHg at room temperature is more than half an atmosphere: an open dish empties itself. That is why the film sets, and it is why the room fills.

Its vapour is heavier than air. CAMEO states it directly. A dense flammable vapour does not rise and disperse; it runs down and pools, so the ignition source that matters may be at floor level and some distance away.

Its flash point is −49 °F. There is no ambient temperature at which the space above the liquid is too cold to burn, and the explosive range runs from 1.9 to 36.0 per cent in air, which is unusually wide. NIOSH classes it a Class IA flammable liquid, the most volatile category it uses.

It is an anaesthetic. H336, may cause drowsiness or dizziness, is a clinical understatement of a compound that was used as a surgical anaesthetic for a century. The hazard is not only that it burns; it is that a person overcome by the vapour is in a room that is about to.

Properties

A colourless, extremely mobile liquid, lighter than water at a specific gravity of 0.71, boiling at 94 °F — NIOSH’s bracketed note is that it is a gas above that temperature — and freezing at −177 °F. It dissolves in water to about 7 per cent and mixes with almost every organic solvent there is.

The property that is not on any GHS block is peroxide formation. NIOSH’s note reads that the substance tends to form explosive peroxides under the influence of air and light. The peroxides are much less volatile than the ether, so evaporating or distilling a peroxidised bottle concentrates them in what is left behind. This is the reason that laboratories date ether bottles and discard them by the calendar rather than by how full they are, and it is a hazard that grows while the container sits unopened.

Handling

Three authorities give three answers, and one of them is “none”. NIOSH publishes no recommended exposure limit for ethyl ether and refers the reader to its Appendix D, Substances with No Established RELs. OSHA’s permissible limit is 400 ppm, or 1,200 mg/m³, over eight hours. HSE’s EH40 sets a long-term limit of 100 ppm (310 mg/m³) and a short-term limit of 200 ppm (620 mg/m³), with no notation. That is a fourfold difference between the two figures that exist, and an absence where a third should be. The course quotes EH40, because EH40 is the British list this course is written against, and states the others rather than harmonising them.

It also states the limitation the Level D policy already identified: an exposure limit measures the wrong thing here. EH40’s 100 ppm is a toxicological figure about breathing ether over a working day. The explosive range starts at 1.9 per cent, which is 19,000 ppm — nearly two hundred times the limit. Long before an ether atmosphere is a fire, it is far past the point at which anyone should be in the room; the fire hazard and the health hazard simply do not share a scale.

NIOSH’s symptom list is irritation of the eyes, skin and upper respiratory tract, then dizziness, drowsiness, headache, excitement and narcosis, with nausea and vomiting, and the eyes, skin, respiratory system and central nervous system as target organs.

☠Why Level D

The Level D policy covers wet collodion under “the dangerous solvents” and notes that, when it was written, the course had not found a full hazard record for diethyl ether in its own corpus and therefore would not print a flash point or an explosive range it had not read. This entry closes that gap: the NIOSH Pocket Guide entry is in the corpus and has been read, and the figures above come from it. The classification does not change, and the policy page’s argument did not depend on the gap.

What the figures add is precision about why. The hazard is an ignition hazard, not a dose hazard, and it is not controlled by gloves, by a mask or by working carefully. It is controlled by removing every ignition source from a volume that a heavier-than-air vapour will find on its own — which is what a flammable-solvent facility is, and what a domestic room is not. The historical operation makes it worse in the specific way that matters: the plate is poured by hand, in the open, in a small dark space where a person cannot see where the vapour has gone.

The one operation that would take this entry out of Level D is opening the bottle, and there is no version of the process that avoids it.

Waste

Nothing here produces waste, because nothing here is used. The general rule is worth stating anyway, because it is the rule for every flammable organic solvent a reader might meet: it does not go down a drain, it is not disposed of by letting it evaporate, and a bottle old enough to have formed peroxides is handed intact to a licensed route rather than opened, decanted or distilled. GOV.UK’s household guidance routes hazardous waste from a home to the council’s collection service. Check your local regulations; they govern.

History

Ether is older than photography and reached it already in use elsewhere. The period name — sulphuric ether — records how it was made rather than what it contains, and Archer uses it throughout. It arrived in photography as the solvent that, with alcohol, would dissolve nitrated cotton; ChEBI’s summary of the compound records its other career in one phrase, inhalation anaesthetic, which is the clinical form of what H336 says in regulatory language.

Its photographic career ended with the wet plate, for reasons that had nothing to do with safety: gelatin dry plates could be bought ready-made, kept, and developed at leisure, and no solvent was involved at any point. Ether went out with the process, and what replaced the whole assembly was a protein that dissolves in warm water. That is worth holding on to when reading a period manual: the first thing modern photography did with its freedom was to stop using solvents.