Gold-acetate toner

The gold bath the albumen period used more than any other, and the one a modern printer is least likely to choose: it will not tone anything for the first twenty-four hours. That delay is not a defect of the recipe. It is the reduction of gold(III) to gold(I) happening slowly, in an alkali too mild to hurry it, and it is the clearest demonstration in the formulary of what an alkaline gold toner actually is.

Ingredient	Quantity	Form the source specifies
Sodium acetate (anhydrous)	20 g	fused, which is the anhydrous salt
Chloroauric acid	40–50 mL of a 1% solution	printed as "1% gold chloride solution", at a range rather than a single figure; the course's reagent for that name in the photographic literature is chloroauric acid
Water	to make 1000 mL

Purpose

To tone an albumen or salted paper print to a purplish or bluish black, in an alkaline bath, and to hold the image through the fixer. Reilly’s contrast is with platinum toning, which gives brown and brownish-black tones where gold gives purplish and bluish-black ones.

Kodak’s 1928 primer explains why an alkaline bath at all, and it is a statement about particle size rather than about pH: the rate at which the metal is deposited is very important, finely divided gold is red, which is not as pleasing as the blue gold obtained by more rapid deposition, and to ensure rapid deposition the bath must be kept alkaline. Borax or sodium acetate is consequently added to the gold chloride to make a toning bath.

Recommended uses

Glossy albumen paper. At 0.4 to 0.5 g of gold chloride per litre this bath sits exactly in the band Reilly gives for glossy albumen — the strongest of his three classes — and above the 0.1 to 0.2 g/L he gives for matte salted papers, which would over-tone in it.

Where a bath is wanted that can be kept and topped up. Reilly singles the acetate bath out: most alkaline gold baths are one-use and go inactive spontaneously after a few hours, but baths made with sodium acetate can be used repeatedly if strengthened with additions of gold stock.

Where the toning is to be leisurely and watched. Reilly’s own argument for a slow bath is that a leisurely pace allows each print to receive individual attention, and that too active a toner — from too much gold or too high a pH — does not produce pleasant tones and is harder to control.

Not where the print has to be toned today. See Behaviour.

When another formula is preferable

• For matte salted paper, arrowroot and the porous surfaces, a weaker bath: the gold-borax toner as the supplier’s kit publishes it, at 0.157 g/L, sits in Reilly’s band for those papers. This formula would over-tone them.
• Where the bath must work the same day, the gold-thiocyanate toner, which is mixed cold and used at once because the sulfur ligand does in minutes what an acetate does in a day.
• Where the print is silver gelatin, Kodak’s GP-1 or T-21; no source read for this course gives times for an acetate bath on a developed-out paper.
• Where a brown or a neutral black is wanted rather than a purple, the platinum toner — which the course publishes as chemistry only, at Level C, and does not ask anyone to use.

Mixing

One litre, one order, and then a day’s wait.

1. Fused sodium acetate, 20 g, dissolved in most of the water.
2. 40 to 50 mL of a 1 per cent gold chloride stock.
3. Water to make one litre.
4. Leave it for about twenty-four hours, until it has gone from yellow to colourless.

Reilly’s modern simplification is worth knowing, because the older literature will tell you otherwise. Two approaches exist: one neutralises the gold stock with calcium carbonate — that is, chalk — before the toner is compounded, which removes free acid without making the stock alkaline; the other relies on the alkaline substances of the formula to overcome the gold stock’s acidity. For modern practice Reilly recommends the second: use the gold stock in its acid condition, and take care that approximately the same mildly alkaline condition is reached in each batch.

🧮What the range means, and why it is a range

40 mL × 1% = 0.4 g per litre

Gold chloride, at the bottom of the range

50 mL × 1% = 0.5 g per litre

Gold chloride, at the top

20 g per litre

Sodium acetate

0.4 to 0.5 g per litre is not a tolerance, it is Reilly’s own strength rule for glossy albumen paper, printed on the same pages. The formula’s range and the rule’s range are the same range, which is a rare thing to be able to say about a historical formula: the recipe and the reasoning behind it were published together.

The acetate is in very large excess over the gold. At 82.03 g/mol for the fused salt it gives 244 mmol/L against the gold’s roughly 1.2 to 1.5 mmol/L — about a hundred and seventy to one, which is the ratio of a buffer to what it buffers rather than of a ligand to a metal. Compare the gold-borax toner at about forty-five to one: this bath is a much larger reservoir of alkali at a much milder strength, which is consistent with a slower ripening and a bath that can be replenished rather than thrown away.

Behaviour

It ripens, and until it has, it does nothing. Reilly: some baths found in the older literature may take hours or even days to decolorize and become usable, and the most common of these is the sodium acetate toner, which generally requires 24 hours to “ripen” before it can be used.

The colour of the bath is the test. The stock gold solution retains a yellow colour while still in the relatively inactive acidic state; when it has passed into the more active state through contact with alkaline substances it becomes colourless, and this decolorization is the best guide to the state of the toning bath.

More alkaline is not better and Reilly is emphatic. A bath made too alkaline tones more quickly but loses its activity much more rapidly; too active a toner, whether from too much gold or too high a pH, does not produce pleasant tones and is more difficult to control; and making the toner too alkaline results in baths that still contain a great deal of gold but no longer tone prints.

It can be replenished, unlike most alkaline gold baths. Reilly’s general statement is that most alkaline baths are intended for one-use toning and become inactive spontaneously after a few hours, with no clue other than the cessation of toning action to indicate exhaustion — and then the specific exception: baths made with sodium acetate can be used repeatedly if strengthened with additions of gold stock.

Toning takes 3 to 15 minutes at 17 to 20 °C with constant agitation, and it is carried well past the first visible change.

Image characteristics

Purplish and bluish-black, in Reilly’s comparison with platinum’s brown and brownish-black.

The colour depends on how fast the gold arrives. Kodak’s 1928 primer states the rule that governs every alkaline gold bath: finely divided gold is red, and the more pleasing blue gold comes from more rapid deposition. A slow, weakly alkaline bath and a fast, strongly alkaline one deposit differently sized gold particles and therefore different colours — which is the same physics that governs the colour of the silver image itself.

A print judged flat in a tray will be judged wrong. Reilly says so directly, and prescribes weak incandescent light and, for glossy albumen, an end point read by transmitted light: continue until only the shadows retain their original warm colour.

Under-toning is the commonest fault, because the first visible change is well short of the end point.

The mechanism

This is Ware’s second route to gold(I), and this bath is the slowest example of it in the formulary.

⚗An alkali instead of a ligand

Gold in the salt you buy is gold(III), and silver oxidises only to silver(I), so a plain gold(III) bath spends three silver atoms for every gold atom deposited: it bleaches the print faster than it tones it, and Reilly’s description of that result is flat, lifeless and reddish. The equations are on the chloroauric acid page.

A useful gold toner works with gold(I), one silver for one gold. Ware’s two routes are a sulfur ligand — thiosulfate, thiocyanate or thiourea, which both assists the reduction and stabilises the product — or a plain mild alkaline buffer such as acetate, borate, carbonate or chalk, in which gold(III) slowly oxidises water instead, over as much as twenty-four hours.

Twenty-four hours is Ware’s figure and it is also Reilly’s ripening time for this exact bath, arrived at from the bench rather than from the chemistry. That agreement is the strongest evidence in this formulary that the alkaline route is what its account says it is.

Why more alkali makes a worse bath rather than a faster one. A more alkaline bath reduces its gold faster, which is what Reilly means by tones more quickly — but the same reduction continues past gold(I) towards metallic gold in the tray, which is what he means by loses its activity much more rapidly and by a bath holding a great deal of gold that no longer tones. The acetate’s job is to be alkaline enough and no more.

Why toning is always followed by fixing. The chloroauric acid page notes it in a clause: toning in a chloride bath leaves silver chloride in the paper. That is why Reilly’s sequence is tone, five-minute wash, fix.

Why a trace of fixer destroys it. Reilly is blunt — the toner solution is ruined by even a trace of fixer — and the reason is on the gold page: thiosulfate is a far stronger ligand for gold than an acetate buffer is a reducing environment, and it takes the gold out of play.

Function of every ingredient

Sodium acetate, 20 g, fused. The alkaline buffer, and the whole of the formula apart from the gold. In a mild alkali, gold(III) reduces itself at the expense of the water; the acetate’s job is to hold the bath at a pH where that happens steadily rather than violently. More makes a bath that ripens faster, tones faster and dies faster — Reilly’s three consequences of over-alkalinity, of which the third is a bath full of gold that tones nothing. Less leaves the gold stock’s own acidity unneutralised, and an acid gold bath stays yellow and inactive. Note the form: Reilly specifies fused sodium acetate, which is the anhydrous salt; the trihydrate is about 44 per cent water by mass, so 20 g of it would be substantially less acetate, and the two are not interchangeable by weight.

Chloroauric acid, 40 to 50 mL of a 1 per cent stock, so 0.4 to 0.5 g per litre. The gold, and the only substance that ends up in the print. Reilly prints it as “gold chloride”, and the course’s reading of that name in the photographic literature is this substance rather than gold(III) chloride proper — the two are about 50 and 64.93 per cent gold, so they are not interchangeable by weight. The quantity is a range, and it is recorded as one because it is one: Reilly’s own strength rule puts glossy albumen at 0.4 to 0.5 g/L and the formula’s range is that rule. Take the lower end for a less glossy surface and the upper for a fully glossy one. More than the range over-tones and, past a point, deposits gold superficially so that the layer is largely removed in the fixer. Less is what happens as prints go through the bath, and it is what the replenishment answers. Note the form: 40 mL is not a quantity and 40 mL of a 1 per cent solution is.

Water, to make one litre. Reilly gives a make-up volume, which most of the gold formulas in this batch do not, so every strength on this page is a published strength rather than a computed one.

Interactions

With fixer, absolutely. Even a trace ruins the toner. Separate tongs, and a print that is washed before it comes in.

With free silver nitrate on a freshly printed sheet, which will take gold out of the bath before the image gets any. The intermediate wash that every printing-out process specifies is what prevents it.

With acid, which takes the buffer out of its working range and returns the gold to its yellow, inactive state.

With calcium carbonate, deliberately, in the older literature. Reilly describes the practice: chalk was used to neutralise the free acid of the gold stock before the toner was compounded. It does not make the stock alkaline; it removes what the acetate would otherwise have to overcome. Reilly recommends against bothering.

With metal. Ware records that these gold compounds are corrosive and oxidising and attack most metals. Glass and plastic throughout.

With light and organic matter, both of which reduce dissolved gold.

With a platinum toner, deliberately. Reilly’s combined route uses a gold bath first and a platinum bath after it; his instruction names the borax bath rather than this one, and it is on the platinum toner page.

Variants

Reilly’s Borax Bath, printed on the same page: borax 10 g, 1 per cent gold chloride 40 mL, water to make 1 litre — 0.4 g/L of gold, the same as this bath’s lower end, in a different alkali. The gold-borax toner page carries a modern supplier’s version of the same architecture at 0.157 g/L, which is a much weaker bath for a much more porous paper. Three published borax and acetate baths, three gold strengths, one strength rule that explains all three.

Reilly’s Thiocyanate Toner: sodium thiocyanate 15 to 20 g, 1 per cent gold chloride 60 to 80 mL, water to 1 litre. The sulfur-ligand route, at 0.6 to 0.8 g/L — above his own strength rule, a gap the sodium thiocyanate page notes and does not reconcile.

The chalk-neutralised baths of the older literature, described above. No quantities are printed here because Reilly describes the practice without giving one.

No course variant is offered. The formula is published with a range that is itself the design decision, and there is nothing to make safer: both ingredients are ordinary and the bath is cold.

Safety

Level B, and the whole of it comes from the gold. Sodium acetate is Level A; chloroauric acid is Level B, and its page carries the classification and the controls.

The controls that matter here: nitrile gloves whenever the gold solid or its stock is handled — the aggregated classification gives severe skin burns and serious eye damage unanimously — chemical splash goggles for the solid and the stock, plastic rather than metal for stirrers and trays, and hands washed before eating.

Nothing in this formula is hot, oxidising, sulphidic or acidic in any dangerous sense. Alongside the sulphide and selenium toners it is a remarkably ordinary bath, and the only reason it is not Level A is that a gold salt is corrosive.

The gold is weighed only if you make your own stock. Buying a 1 per cent solution removes the one powder this formula would otherwise put on the bench.

Storage

The bath is kept and replenished, which is unusual among alkaline gold toners and is Reilly’s specific claim for the acetate.

In the dark, because light reduces dissolved gold, and away from organic matter for the same reason.

In glass or plastic, never metal, including the closure.

No shelf life is published for the ripened bath and none is invented here. What Reilly gives instead is a test and a warning: a colourless bath is active, and a bath that has stopped toning has stopped without any other sign.

Label the stock with its strength and the bath with the date it was mixed, because the twenty-four-hour ripening makes the mixing date part of the formula.

Incompatibilities

Fixer, in the bath. Even a trace.

Acids, which return the gold to its inactive state.

Metals, with the gold.

Light and organic matter, with the stock and the bath.

Free silver nitrate, carried in on an unwashed print.

Sulphide and selenium toners, in the waste bottle.

Waste

A gold-bearing stream that has picked up a little silver, in one-litre quantities.

Not acidified, and not combined with any sulphide or selenium waste.

The larger silver stream on a printing-out process is the fixer and the first wash, not this — which is the stream open question 1.3 and the disposal ruling are about.

Collect it, label it, and follow the silver-bearing waste SOP, the general chemical waste SOP and the disposal ruling. Local regulation decides, and this course cannot tell you what it says where you are.

Troubleshooting

The bath is still yellow. It has not ripened. Reilly’s figure is about twenty-four hours; a bath that is still yellow after that has too little alkali, or the acetate did not dissolve.

The bath is colourless and nothing is toning. Reilly’s other failure and the more expensive one: too alkaline, so the gold has gone past the useful state. The bath still contains a great deal of gold and will never tone another print.

The print went red rather than purple. Deposition too slow, per Kodak’s 1928 rule that finely divided gold is red. A more alkaline bath, or a fresher one, deposits faster and bluer.

The print looks toned in the tray and untoned when dry. Reilly warns that judging prints lying flat in a tray is deceptive; the end point for glossy albumen is read by transmitted light.

The bath stopped after two prints. If it is not an acetate bath it was probably a one-use bath all along. If it is, replenish with gold stock.

Toning stopped suddenly and completely, with no other sign. Reilly names this exactly: there is no clue other than the cessation of toning action.

Stains, or a bath that died at once. Fixer contamination, or free silver nitrate from a print that was not washed enough before toning.

Experiments

Watch the bath ripen. Mix the formula and photograph it against a white card every two hours for a day, testing a print strip alongside each time. Reilly gives twenty-four hours and a colour test; the curve of activity against time has never been published and it is an evening’s work spread over a day.

Put the three alkalis against each other. The acetate bath, Reilly’s borax bath and the supplier’s borax kit, all on the same paper. Same metal, same route, three alkalis and three gold strengths; the differences in ripening time and colour are the whole content of the alkaline gold literature.

Test the over-alkalinity claim. The formula at 10, 20 and 40 g of sodium acetate, each ripened and then used on identical prints, with the bath’s colour recorded. Reilly predicts faster toning and much shorter life as the alkali rises, ending in a bath full of gold that tones nothing.

Test Kodak’s colour rule. Deposition rate is said to set the particle size and therefore the colour: red for slow, blue for fast. A weak, barely ripened bath against a strong, fully ripened one, on twin prints, is that claim as a pair of photographs.

Compare the routes at matched gold. This bath at 0.4 g/L against a thiocyanate bath diluted to the same gold. Alkaline buffer against sulfur ligand, one metal, one concentration — and the thiocyanate bath is also dissolving silver while it plates, which should show first in the highlights.