Glycin

Dilute a glycin developer to a tenth and it takes very close to ten times as long. Almost no other developing agent is that well behaved, and the property is the reason glycin survived into the twentieth century as the tank and stand developer of choice while faster agents took the tray.

In photography

A slow, clean, neutral developer. Wall’s 1912 dictionary calls glycin “a very clean negative developer, and owing to its non-staining qualities specially suitable for stand development”, and adds that it “is the first favourite in popular esteem for this method of working”. His 1924 formulary is blunter still: “a slow-working very clean developer giving images of a neutral grey colour”. Abney, in 1905, describes the working behaviour: the image develops steadily and gains density as the detail is brought out, yielding negatives of considerable vigour with clear shadows. Set that against the pattern Kodak’s 1928 primer gives for the agents it does list — a high reduction potential such as Elon’s makes the image flash up all over at once, a low one such as hydroquinone’s brings the highlights up first — and glycin sits with neither extreme: it is simply slow all through.

Why the dilution rule holds. Wall states the rough rule that a developer’s energy varies with its dilution, then the exception: Mees had shown a big variation from that rule with metol and hydroquinone, and also when air is dissolved in the water, but “with glycin and pyro-soda time seems proportionate to dilution”. Wall’s 1924 book puts numbers on the failure of the rule elsewhere. Wratten & Wainwright measured photometrically that a plate needing three minutes in rodinal at 1+20 needed, at 1+200, not the thirty minutes arithmetic predicts but 42 minutes in air-free distilled water, 46 in ordinary distilled water and 52 in tap water — and that “pyro-soda and glycin seem to be the only developers that are not affected by the water”.

That is the whole case for glycin in a tank. A developer whose time you can compute from its dilution, and which does not change its mind when the water does, is a developer you can leave alone for an hour. The British Journal Photographic Almanac prints Hübl’s directions for exactly that: one ounce of the concentrated glycin stock in 80 to 90 ounces of water with 80 minims of ten per cent bromide, in which “a properly exposed plate should make its appearance in 15 or 20 minutes, and obtain full density in several hours”, with caustic soda added for under-exposure and more bromide for over-exposure.

Restrainer and temperature. Wall’s tables of the Watkins factor — total development time divided by the time the image first appears — give glycin with sodium carbonate as 8 and with potassium carbonate as 12, against 30 for metol, 14 for metol-hydroquinone and 5 for hydroquinone with minimum bromide; Wall’s 1924 list repeats glycin-soda 8 and glycin-potash 12. A small factor means the image appears late in its own development, which is what a slow, even-working agent does. The alkali matters as much as the agent: swapping potassium carbonate for sodium raises the factor by half. Abney adds that bromide is not necessary with correctly exposed plates and that with over-exposed ones it should be added cautiously, “as even a very small proportion will retard development considerably”. Wall’s temperature coefficients — the ratio of times over a 10 °C interval — put glycin in tabloid form at 2.3, beside 2.25 for hydroquinone and 1.9 for metol-quinol, so a long stand development in a cold darkroom is not the same long development in a warm one.

In papers and for line work. Wall lists glycin among the developers usable on alpha development-printing papers, with hydroquinone preferred for warm tones, and Abney records that the makers recommended it for line negatives on dry plates. The 1906 almanac prints Sturenberg’s glycin developer for reproduction work: 20 g of glycin against 100 g of sodium sulfite and 60 g of sodium carbonate in a litre, with potassium bromide whose quantity the scan does not render legibly. The same volume carries Lüppo-Cramer’s comparison of colour fog under heavy bromide, in which pyro and adurol gave appreciably more, “edinol and glycin, less; pyrocatechin, none; metol, a trace” — the experimental version of Wall’s word clean.

⚗Not a dihydroxybenzene at all

Glycin is easy to file with hydroquinone and catechol because it turns up in the same tables, and it belongs to a different family. ChEBI describes it as the N-(4-hydroxyphenyl) derivative of glycine, synthesised by reaction of p-aminophenol with chloroacetic acid.

C₆H₇NO + C₂H₃ClO₂ → C₈H₉NO₃ + HCl

ChEBI's route: p-aminophenol and chloroacetic acid, balanced here by the course

So glycin is p-aminophenol carrying a carboxymethyl group on its nitrogen, an aminophenol rather than a phenol with two hydroxy groups, and it is not the amino acid glycine — PubChem’s own record carries the warning.

Not sourced here. Why that added acid group should slow the agent down, why it should fog so much less than pyro under bromide, and how the electron reaches the silver, are all outside what the course’s sources establish. Nor does the IUPAC dissociation-constant dataset carry a pKa for this molecule, so its alkali dependence is read off the formulas — every one of them carries carbonate or caustic potash — and from Kodak’s general statement that a developing agent will not work without alkali and that the developer’s energy follows the amount present.

Properties

C₈H₉NO₃, relative molecular mass 167.16, CAS 122-87-2, PubChem’s IUPAC name 2-(4-hydroxyanilino)acetic acid. Haz-Map records the Merck Index as giving a shiny solid and an Alfa Aesar safety data sheet as a white or light brown powder — and that spread of colour is itself informative, because Abney describes fresh glycin as a white crystalline powder that turns brownish-black when carelessly kept and loses its developing power along with its colour.

Solubility is the gap on this page. PubChem holds no solubility record for CID 67149 at all; the request returns nothing. What the course can source is period practice, which is consistent: Abney dissolves the sulfite in hot water first and adds the glycin and the potassium carbonate to it, and Hübl’s concentrated stock puts 250 g of glycin into a litre of boiling water that already holds 625 g of sodium sulfite, then adds 1,250 g of potassium carbonate in small quantities to make a thick cream. Nobody in these sources dissolves glycin in plain water. Abney does say that when fresh it is “readily soluble in water”, and the course records the contradiction rather than choosing between an isolated adjective and the unanimous practice of dissolving it into a strong sulfite solution. The order — preservative first, then agent, then alkali — is the same one Kodak Limited’s 1949 handbook gives for Elon, which is only slightly soluble in sulfite solutions without alkali.

Hydrates and stability. No hydrate of glycin appears in any source the course holds, so there is no conversion factor to give. The stability story is entirely about oxidation: dry, dark and closed it keeps; Abney’s stock solution “will keep well”; open to the air it browns and dies. That is the same failure mode as pyro and hydroquinone, and the same three defences apply — a preservative in the bottle, minimum air space, and the alkali kept out until use.

Handling

The aggregated ECHA notifications give Warning, one pictogram and three statements: H315, causes skin irritation and H319, causes serious eye irritation, both at 100 per cent, and H335, may cause respiratory irritation, at 97.7 per cent. The number that deserves as much attention as the percentages is the base: 44 reports across 4 notifications. Hydroquinone’s classification rests on 2,485 reports across 36 notifications and a harmonised entry in European law; glycin’s rests on four notifiers agreeing with each other. The PubChem record carries no harmonised classification, and the course found glycin in neither the NIOSH Pocket Guide nor HSE’s EH40 list and could locate no CAMEO datasheet and no International Chemical Safety Card — so there is no workplace exposure limit, no reactivity profile and no incompatibility list. HSE’s own introduction to EH40 makes the point the course needs here: the absence of a substance from the list of workplace exposure limits does not indicate that it is safe. ChEBI separately records a role as an allergen, and HSE’s HSG262 supplies why that matters at tray dilutions — once a person is sensitised, small amounts provoke the reaction and preventing further exposure is the only remedy left.

Why Level B. A literal reading of the rubric would allow Level A: irritation of skin, eyes and airway is exactly the ceiling Level A sets, and the quantities are those of a home darkroom. Two things push it up. Level B names “fine powders that must not be inhaled”, and H335 at 97.7 per cent with a weighing step is that case; Level B also names sensitisers, and an allergen role is close enough to warrant the same handling. The third reason is not in the rubric but belongs in the judgement: for metol and hydroquinone the course can point at an exposure limit and a manufacturer’s control regime and say that the operation is understood. For glycin it cannot, and a substance the regulators have barely looked at is not thereby a mild one.

⚠Safety

Weigh it with extraction or inside an enclosure and raise no dust; the airway statement is the one notified almost unanimously by a very small group of notifiers, and there is no exposure limit to measure against. Nitrile gloves and eye protection for solutions, tongs rather than fingers in the tray. Keep the tin closed, dark and dry — the brown powder is not merely spent, it is an unknown mixture of oxidation products with no classification of its own. The incompatibilities list on this page is empty because nothing sourced fills it, not because the course has established that nothing reacts with it.

Waste

Spent developer, in its own labelled bottle. The organic load is the issue and the silver is not: Kodak’s J-300 guidance records that developer solutions carry negligible silver, so there is no recovery to be had and every reason to keep the bottle away from the fixer, which does carry silver worth recovering. Nothing in the aggregated notifications puts an aquatic hazard statement above PubChem’s display threshold — and nothing puts an aquatic datum there either, so this page cannot tell you that the stream is harmless to a watercourse; it can only tell you that no notifier has said so either way. ILFORD’s guidance for domestic users in the United Kingdom is to bottle each chemical separately, label it, mix nothing, and leave it in the chemical cupboard at a Household Waste and Recycling Centre. Check your local regulations; they decide.

History

Glycin came out of the same laboratory as metol. Eder credits the discovery of metol, amidol and glycin as developers to the chemist Dr A. Bogisch in the photographic department of the chemical factory of J. Hauff at Feuerbach, near Stuttgart, which had turned to developer preparations from about 1890; his notes add ortol to the same list. Eder dates metol’s introduction into practice to about 1893 and gives no date for glycin, and the course could not source one.

What happened next can be read off the manufacturers’ own lists. Kodak’s 1928 American primer names the commonest developing agents as pyro, hydroquinone, Elon, para-aminophenol and diaminophenol, and glycin is not among them. Kodak Limited’s 1949 British handbook does stock it, under the trade name Kodurol, with the note that “‘Kodurol’ is parahydroxyphenyl glycine, also commonly known as glycin” — the same handbook that explains ‘Elon’ and ‘Kodalk’ in the same breath. And in the current datasheets the course holds, from ILFORD, Foma, Adox and Bergger, glycin appears nowhere at all.

The reason to know it anyway is the reason Wall gave in 1912. Stand and semi-stand development — long times, high dilutions, minimal agitation, and a compensating effect on the highlights — has come back into practice, and glycin is the agent whose period literature was written for it, with measured evidence that its times scale as its dilution and do not care what is dissolved in the water. That is a stronger claim than most modern developers can make, and it is a hundred years old.