Kodak HE-1

This page exists because the formula is published, sourced and important to understand, and not because the course recommends using it. A hypo eliminator does not displace thiosulfate out of a print; it destroys it chemically, in the presence of a silver image, with an oxidising agent. Kodak published this one with a capacity, a test and three warnings. Wall was already sceptical of the whole class a quarter of a century earlier. Read both before you mix it.

Ingredient	Quantity	Form the source specifies
Water	500 mL	the two solutions are added to it
Hydrogen peroxide	125 mL	of a 3 % solution — “10 volume, as purchased”
Ammonia solution	100 mL	of a 3 % solution, made by diluting 9 parts of .880 ammonia to 100 parts
Water	to make 1000 mL

Purpose

To convert the thiosulfate a print retains after washing into something inert, and so to make the last of it easier to remove. Kodak’s own sentences are precise about both halves of that claim: HE-1 used as directed converts the hypo to inert sulphate and also facilitates its removal.

The handbook is equally clear about when the problem arises. Hypo eliminators are not usually required in processing negative materials; in the case of prints, however, traces of hypo are tenaciously held by the paper fibres and may lead to fading of the image on long keeping under adverse conditions. That diagnosis is the same one the sulfite washing aid answers, and Reilly puts it in the same terms — water alone is a poor remover of low levels of thiosulfate from prints.

Two families of answer follow from one diagnosis, and the difference between them is the argument of this page.

Recommended uses

The course’s recommendation is the sulfite washing aid, not this. That is stated first because the rest of this section is a faithful account of Kodak’s own directions, and it would otherwise read as endorsement.

Kodak’s directions, in full, are:

1. Wash the prints for about 30 minutes at 18 to 21 °C, in running water flowing rapidly enough to replace the water in the vessel completely once every five minutes. Increase the time at lower temperatures; double it for double-weight prints.
2. Immerse each print for about six minutes at about 21 °C in the eliminator.
3. Wash for about 10 minutes before drying.

For plates, films and lantern slides, dilute with 10 parts of water, otherwise the emulsion may be rendered unduly tender — which is Kodak telling you that at full strength this bath attacks gelatin.

Fifty 8 × 10 prints per gallon, which the handbook equates with 4 litres.

When another formula is preferable

• The one per cent sulfite washing aid, in almost every case. It displaces thiosulfate rather than oxidising it, it introduces nothing into the paper that can attack silver, and it is published with a mechanism, a time and an exhaustion figure by a conservation source.
• A longer wash, in most of the rest. Wall’s judgement is the one the course adopts: a negative or print can be practically freed from hypo in half an hour by proper washing, so the use of these preparations is only allowable in cases of great pressure of time or shortage of fresh water. Note that Kodak’s own directions put a 30-minute wash before the eliminator, so HE-1 is not a way of avoiding that wash.
• Nothing at all, for a printing-out paper. The image silver of an albumen or salted-paper print is finely divided and vulnerable, and an oxidising bath is the last thing it should meet. Reilly’s sequence for those materials is the sulfite bath and a long wash.

Mixing

Water first, then the two solutions, then make up. There is no hazardous order here — the peroxide and the ammonia are both dilute by the time they meet — and the handbook gives no mixing temperature.

The hazard is upstream of the formula. Neither line names the substance you buy. The peroxide is a 3 per cent solution, which the footnote identifies as the 10-volume solution sold over the counter, so that line is 125 mL of the bottle as it comes. The ammonia is a 3 per cent solution that you must make, by diluting 9 parts of .880 ammonia to 100 parts of solution — and .880 ammonia is the strongest grade there is.

🧮Reading the two footnotes, and checking them

The peroxide. “10 volume” is an old British strength: one volume of the solution releases ten volumes of oxygen on decomposition. Kodak equates it with 3 per cent, which is the conventional equivalence and the strength of the peroxide sold for domestic use.

125 mL × 3 % = 3.75 g of H₂O₂ in a litre, or 0.11 mol/L

Peroxide delivered

The ammonia. The ammonia page gives the density table for the aqueous solutions, in which 0.880 corresponds to 35 per cent w/w — which is what the old British name “.880 ammonia” refers to, the density rather than the strength.

9 mL × 0.880 g/mL × 0.35 = 2.77 g of NH₃ in 100 mL, so about 2.8 % w/v

Checking Kodak's 3 per cent

100 mL of that = 2.77 g of NH₃ in a litre, or 0.163 mol/L

Ammonia delivered

Kodak’s rounding to “3 per cent” is fair, and the arithmetic is worth doing because the dilution instruction is given as a volume ratio of an unnamed strength and only the density table makes it a quantity.

The ratio that matters. 0.11 mol of peroxide against 0.163 mol of ammonia: the bath is alkaline, with the oxidant the limiting reagent.

Behaviour

It works, on Kodak’s own account, and the handbook publishes the test that proves it. Process an unexposed white sheet of the same paper and weight alongside the batch; after the final wash, cut a strip, immerse it in a 1 per cent silver nitrate solution for about three minutes, rinse, and compare it wet against the untreated part of the same sheet in subdued light. No colour difference means the hypo has gone; a yellow-brown tint means it has not. Kodak adds two cautions: silver nitrate stains skin black, and the same yellow-brown effect can be produced by hydrogen sulfide or wood extracts in the water supply rather than by hypo.

It has three published side effects, and Kodak’s own remedies for them are as informative as the formula.

• Prints tend to stick on the belt of belt driers. Kodak’s remedy is a 3-minute bath in 1 per cent formaldehyde before drying. The course does not adopt that remedy. Formaldehyde is excluded from this course, and the emulsion literature excluded it before the toxicologists did; see the formaldehyde page.
• A slight change of image colour. Kodak’s remedy is to add 1 g of potassium bromide per litre of HE-1. A bath that changes image colour is a bath that is reaching the image.
• A slight yellowing of the whites. Kodak’s remedy is to bathe the prints in 1 per cent sodium sulfite for two minutes before the final wash — which is the washing aid at exactly its published strength, brought in to repair damage done by the eliminator.

Read together, those three notes describe a treatment that reaches the image, alters its colour, yellows the paper and softens the gelatin, and that needs three further interventions to be made safe for use. That is the whole case against the class, written by its manufacturer.

It is not a substitute for washing. Thirty minutes before and ten minutes after, in Kodak’s own directions.

Image characteristics

It has them, which is the problem. Every other accessory solution in this formulary is required to leave no signature at all. This one comes with a manufacturer’s note that it can change image colour, and with an additive to stop it doing so.

And its worst effect is invisible at the time. If Wall is right about the products (see The mechanism), what is left in the paper is tetrathionate, which is exactly the species the thiosulfate page records as sulfiding silver and attacking an image. A treatment applied for permanence that leaves behind an image-attacking anion would be the worst possible outcome, and it would not be visible for years.

The course cannot establish from its corpus whether that happens under HE-1’s conditions. That uncertainty is the reason for the page’s position rather than a hedge on it.

The mechanism

What Kodak claims. That the bath converts hypo to inert sulphate. Written as a balanced equation for an alkaline bath, the conversion Kodak’s sentence describes is:

S₂O₃²⁻ + 4 H₂O₂ + 2 OH⁻ → 2 SO₄²⁻ + 5 H₂O

The conversion Kodak states: thiosulfate fully oxidised to sulfate

Sulfate is inert in a print in a way thiosulfate is not: it does not reduce, it does not attack silver, and it washes out readily. If this is what happens, the treatment does what it says.

What Wall suspects. Writing in 1924 about hypo eliminators as a class, he says their action is probably in most cases to convert these salts into tetrathionates. Written as a balanced equation, that is the partial oxidation:

2 S₂O₃²⁻ + H₂O₂ + 2 H⁺ → S₄O₆²⁻ + 2 H₂O

The conversion Wall suspects: thiosulfate oxidised only as far as tetrathionate

The course cannot say which dominates here, and does not pretend to. Both are established thiosulfate chemistry and the two sources name different products; nothing in this course’s corpus establishes which one prevails in an ammoniacal 0.11 mol/L peroxide bath acting on the traces held in a paper fibre. What can be said is that Kodak states the first as a fact about its own product, Wall offers the second as a probability about the class, and that these are two different kinds of claim — a manufacturer’s assertion and a practitioner’s inference — which the course keeps apart rather than merging.

⚗Displacement against destruction

The two families of washing aid answer the same problem in incompatible ways, and the choice between them is a choice about what you are willing to put next to a silver image.

Displacement. The sulfite bath floods the print with a harmless anion in excess and lets ion exchange carry the thiosulfate out. Nothing is oxidised. If some sulfite remains, it does nothing.

Destruction. HE-1 oxidises the thiosulfate where it sits. If the oxidation goes all the way, the residue is sulfate, which does not attack silver. If it stops half way, the residue is tetrathionate, which does. And the oxidant that did it was in contact with the image throughout.

Reilly, writing for conservation in 1980, recommends only the displacement route. Wall, writing in 1924, allowed the destruction route only under pressure of time or shortage of water. The course follows both of them, publishes Kodak’s formula because it is a real published formula that a reader will meet in the older literature, and says plainly that it does not recommend mixing it.

Function of every ingredient

Hydrogen peroxide, 125 mL of a 3 per cent solution, giving 0.11 mol/L in the finished bath. The oxidant, and the active principle. It removes electrons from thiosulfate, converting it either to sulfate — Kodak’s claim — or to tetrathionate — Wall’s suspicion. Everything good and everything doubtful about this formula comes from this ingredient. More would oxidise faster and attack gelatin and image silver harder; Kodak’s own instruction to dilute the whole bath ten-fold for films and plates, lest the emulsion be rendered unduly tender, is the evidence that the concentration is already at the edge of what a gelatin layer tolerates. Less would leave thiosulfate unconverted, which is the failure mode that produces tetrathionate rather than sulfate. Its own page carries the classification for the concentrated material; at 3 per cent, as sold, it is a domestic product, and this bath dilutes that further.

Ammonia solution, 100 mL of a 3 per cent solution, giving about 0.163 mol/L of ammonia. The alkali. It makes the bath alkaline, which is the condition under which peroxide acts as an oxidant on thiosulfate rather than simply decomposing; it also keeps the bath from becoming acidic as the oxidation proceeds, and an acidic thiosulfate solution inside a print is precisely the reaction that produces colloidal sulfur. More ammonia is a stronger alkali against gelatin and more vapour over the tray; less and the bath’s chemistry drifts towards the acid side where the wrong products form. It is the ingredient that sets this page’s safety level, not because of the 3 per cent solution in the tray but because of the .880 concentrate you must dilute to make it.

Water, 500 mL first and then to make 1000 mL. The split is only procedural — the two solutions are added to a part-filled vessel and the volume made up afterwards.

Not ingredients, but part of the published formula: 1 g/L of potassium bromide where the image colour shifts, and a 2-minute bath in 1 per cent sodium sulfite before the final wash where the whites yellow. Kodak prints both as remedies for occasional effects rather than as parts of the formula, and the course keeps them where Kodak put them.

Interactions

With the image silver, which is the whole question. An oxidising bath in contact with finely divided metallic silver. Kodak’s own note that image colour can shift is the observable end of that interaction.

With gelatin. At full strength the emulsion of a film or plate may be rendered unduly tender, on Kodak’s own account, which is why those materials get the bath at a tenth strength.

With the sulfite washing aid, in both directions. Kodak uses the sulfite bath after the eliminator to cure yellowing. But sulfite is itself readily oxidised, so a print carrying peroxide into a sulfite bath spends that bath on the peroxide rather than on ion exchange. Wash between them, which Kodak’s sequence does anyway.

With residual fixer, by design, and with residual silver–thiosulfate complexes too — Wall’s phrase is “the last traces of hyposulphite of soda and the hyposulphites of silver”, and it is the silver-bearing ones that matter most for permanence.

With the wash on either side, as a requirement rather than an option.

Variants

Kodak prints no variant of HE-1, and the course invents none. What the older literature has instead is a whole family of competing preparations, and Wall lists them in the same breath as his objection to all of them:

• Potassium permanganate at 1 per cent, added to water until it gives a pink tinge, the material bathed until the colour is no longer discharged.
• Potassium percarbonate at 1 per cent, sold commercially as Hypax and Hypono.
• Sodium perborate, used the same way.
• Potassium or ammonium persulfate at 1 per cent made alkaline with ammonia, sold as Thioxydant and Anthion.
• Hydrogen peroxide at 5 per cent — which is HE-1’s own oxidant at nearly twice the strength, and shows that Kodak’s formula is a refinement of an existing idea rather than a new one.
• Zinc hypochlorite, after Hart, made from chloride of lime and zinc sulfate.

Every one of them is an oxidising agent, which is the point: the class is defined by its mechanism, and Wall’s objection is to the mechanism rather than to any one preparation. The course publishes none of them as formulas. They are recorded here so that a reader meeting Anthion or Hypax in a period manual knows what it was.

What is not a variant of this is the sulfite washing aid, which belongs to the other family entirely.

Safety

Level B, and the criterion that applies is not the tray.

.880 ammonia is what earns the level. The strongest grade of aqueous ammonia carries H314, causes severe skin burns and eye damage, in 99.9 per cent of over six thousand classifying reports, and H400, very toxic to aquatic life, in 99.8 per cent. Making 100 mL of Kodak’s 3 per cent solution means opening that bottle. Chemical splash goggles rather than glasses, nitrile gloves, an apron, an eyewash within reach, and real ventilation — ammonia vapour is the hazard here as much as the liquid, and the vapour is lighter than air, which is unusual and matters for where an extract should be.

Hydrogen peroxide at 3 per cent, as sold, is a domestic product, and the bath dilutes it further to about 0.4 per cent. The classification on its page is written for the concentrated material and should be read that way. What remains true at any strength is that it is an oxidiser and does not belong near reducing agents, organic solvents or a darkroom’s developer bottles.

The mixed bath is mildly alkaline and mildly oxidising, and its own hazards are modest. Gloves and eye protection, and do not put your hands in it repeatedly.

And the test solution has a hazard of its own. Kodak’s own caution is that the 1 per cent silver nitrate used for the hypo test stains the skin black; the silver nitrate SOP covers handling it.

Storage

Kodak publishes no keeping figures for HE-1, and the course prints none. Its own table of keeping properties, which covers every developer, stop bath and fixer in the handbook, has no row for it.

There is a chemical reason to expect a short life that the handbook does not state: hydrogen peroxide decomposes in solution, faster when alkaline, warm or in contact with metal ions. Mix what a session needs.

Store the .880 ammonia cool, closed, upright, away from acids and from any drain, in a labelled container that has never held food; the ammonia page records that its safety card asks for storage where there is no drain or sewer access. Store the peroxide cool, dark and in its original vented bottle, away from anything it could oxidise.

Label per the labelling SOP.

Incompatibilities

Acids, with the ammonia — the neutralisation is exothermic — and with any thiosulfate the bath has collected.

Reducing agents of every kind, which is to say every developer in this formulary, and sodium sulfite in particular. Peroxide and sulfite destroy each other.

Spent fixer and silver-bearing waste. Do not pour an oxidiser into a thiosulfate waste bottle; the thiosulfate page records that oxidation by almost any oxidising agent gives tetrathionate, and the whole reason to keep silver waste is to recover it.

Metals and metal ions, which catalyse peroxide decomposition. Plastic or glass throughout.

Silver nitrate, which with ammonia is a combination the course treats with great care: the ammonia page records the danger of fulminating silver from ammoniacal silver solutions, and a bath that has held ammoniacal silver is never stored. Keep the eliminator and the sensitising bench apart.

Waste

A dilute alkaline oxidising solution carrying thiosulfate, sulfate, silver–thiosulfate complexes and ammonia. Three of those matter.

Ammonia governs. Its classification is H400, very toxic to aquatic life, in effectively every classifying report, and ammonia is among the parameters most often limited in a discharge consent. The ammonia page sets out what that means for a working solution.

Silver is present, because the bath has been in contact with prints carrying silver–thiosulfate complexes, so this is part of the silver stream.

And it must not be combined with the rest of that stream carelessly, because it is an oxidiser and spent fixer is a reducing agent held for recovery.

Bottle it separately, label it, and follow the general chemical waste SOP together with the silver-bearing waste SOP, both of which cite the disposal ruling. Local regulation decides, and this course cannot tell you what it says where you are.

Troubleshooting

The hypo test still shows a yellow-brown tint. Kodak’s own first alternative explanation is worth trying before the chemistry: hydrogen sulfide or wood extracts in the water supply produce the same stain. Test a strip that has never been near a fixer as a control.

The whites have yellowed. Kodak’s recorded occasional effect. Its remedy is two minutes in 1 per cent sodium sulfite before the final wash.

The image colour has shifted. Kodak’s second recorded effect, and its remedy is 1 g/L of potassium bromide in the bath. Treat it as a warning about what the bath is reaching rather than as a fault to be patched.

The emulsion is soft or tender. You used the bath at full strength on a film, plate or lantern slide. Kodak’s instruction is 1 part to 10 of water for those materials.

Prints sticking to a drying surface. Kodak’s third effect. Its remedy uses formaldehyde and the course does not adopt it; air-dry on screens instead.

Prints fading years later despite the treatment. The outcome this treatment was supposed to prevent, and the one Wall predicted for the whole class. There is no diagnosis available after the fact, which is the strongest practical argument for the displacement route.

Experiments

Test the claim with the maker’s own test. Kodak published both the treatment and a residual-hypo test, so the comparison is available without any further apparatus: three matched prints from one negative, one washed for 30 minutes only, one washed and given HE-1 and a further 10 minutes, one washed and given the sulfite bath and a further 10 minutes. Test all three with 1 per cent silver nitrate against an unfixed control strip.

Then leave them for a year, together, in the same enclosure, and look again. The silver nitrate test reports on thiosulfate; it says nothing about tetrathionate, and the disagreement between Kodak and Wall is about exactly that. A one-year comparison is the only evidence a home darkroom can generate on the question, and it is worth starting now and recording in a laboratory report.

Watch the bath attack gelatin. Kodak says films and plates need the bath at a tenth strength or the emulsion may be rendered unduly tender. Take two scraps of fixed, washed film, treat one at full strength for six minutes and one at 1+10, and compare how each takes a fingernail. Then run the melting-point test from F-5 on both.

Measure the pH drift. Read the fresh bath, then after ten prints, with the pH SOP. Kodak publishes no pH for this formula and the alkalinity is what keeps the oxidation on the right path.