Wolfgang Moersch Photochemie
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Cobalt and iron toning

The combination of cobalt and iron toner is useful to create intensive monochrome image tones from violet to blue. It is also good for split toning.

In this multitude of possible methods it is absolutely necessary to write down exactly what you did in terms of dilution, times of toning, times of rinsing and so on, to prevent future results from being merely arbitrary.

As with all toning, the choice of paper has a huge impact on the toning result. Even the developer you use has an influence.

Included in delivery of the MT12 Cobalt Toner are:
4 concentrated solutions to prepare the Cobalt Toner
2 concentrated solutions to prepare the Ferric Sulphate Toner
200g sodium chloride to prepare a stock solution of a clearing bath (dilute 1+9 for working solution)

Alternatively or additionally to the ferric sulphate toner, you can order ferric citrate toner.

To prepare the Cobalt Toner (ready-made formulation MT12)
destilled water 400ml
Part 1 50ml
Part 2 20ml
Part 3 20ml
Part 4 20ml

Ferric Sulphate Toner (ready-made formulation MT12)
destilled water 400ml
ferric sulphate, 10% solution 20ml
hydrochloric acid, 15% solution 20ml

Ammonia Ferric Citrate Toner (optional)
destilled water 400ml
ammonia ferric citrate, 10% solution 20ml
sulphuric acid, 20% solution 40ml

Cobalt toner alone does not lead to a particularly interesting image tone. Only if you tone additionally in iron, you get colour and density.

Before toning, the print has to be rinsed thoroughly. Between toning in cobalt and toning in iron you have to rinse the print again for at least 20 minutes. This is to prevent a reaction of the bleach substance ferricyanide (part 4) with the iron toner, which would result in staining. As long as they are not contaminated with ferricyanide, both blue toners have an excellent shelf life and can be used until exhausted.

You can shorten the time of rinsing between both toners by half, if you displace the remains of ferricyanide in the emulsion in a weak common salt solution.

Unfortunately, cobalt toner can only be used for 30 to 60 minutes. You should prepare as little working solution as possible for toning. 250ml are enough to tone 24x30cm prints. If you work speedily, you can tone up to 6 or 8 prints. As soon as the toner turns cloudy and dark, it can leave deposits on the print surface. These deposits usually show first on the image borders and on the back of the print. When this happens for the first time, they can be rubbed off with a piece of cotton wool, but further toning with this exhausted working solution can be a risk.

Toning the cobalt image with ammonia ferric citrate results in a continuous monochrome tone from highlights to shadows. Using ferric sulphate can yield to two colours. If toning for longer durations ferric sulphate can lead to a continuous blue-green or blue tone.

cobalt toner + ferric sulphate toner

cobalt toner + ferric citrate toner

Paper: Select VC fibre base (Forte PW14). The times of toning were the same for both prints: cobalt for 2 minutes and iron for 1 minute.

Combining cobalt toner with ferric sulphate toner offers a wider colour spectrum than with ferric citrate toner. In this combination as well, you can achieve a cooler shadow tint by a shorter time in cobalt toner.

The print should stay in cobalt toner for at least 1 minute. Too short durations leave too much silver for the iron toner. The consequence would be monochrome green or blue photographs. If you extend the duration to beyond 4 minutes, however, the cobalt toner has already reached the deep shadows and dichromatic pictures cannot be achieved anymore. On the other side, you can overlay the cobalt image completely. The resulting blue tone is superior to all indirect blue toning in so far as its shadow areas have a much higher density. The range of contrast of the initial print is reached or even surpassed.

The initial print on PW14

cobalt for 2 minutes - ferric sulphate for 1:30 minutes

cobalt for 2:30 minutes - ferric sulphate for 1:30 minutes

as above + after-treatment in ammonia

You can see clearly that extending the duration in cobalt toner leaves only the shadows for the following iron toner (same duration). Only if you doubled the time in iron toner, the dichromatic tone would change to a continuous blue. If you only want to transform the green areas to a reddish blue, treat the toned print in an alkaline solution. It does make a difference whether you use borax, sodium carbonate or ammonia. I like to use ammonia, because it works intensively towards red (here 2ml of a 10% solution in 400ml of water). Borax works more subtly to nuances of delft blue. Since it acts more slowly, it is easy to miss the right moment to stop the process. With a strong reduction in colour you also loose density.

The interaction between the two toners is always the same. Warmtone paper reacts especially colourful. In mixed emulsions with higher content of bromide silver, in pure bromide silver emulsions, and also in iodine silver emulsions the colours are more subtle.

If we will ever have warmtone emulsions available again like those once produced by Forte cannot be known today. For this process, however, we have the ordeal of choice among lots of alternatives.

The following examples were printed on Kentmere Kentona using neutral tone developer (SE4).

cobalt for 3 minutes - iron for 45 seconds

cobalt for 3 minutes - iron for 1:30 minutes

The duration in cobalt toner was the same in both examples. You can see how toning in iron starts taking effect from the shadows. The increase in density (right above) is higher than with shorter duration in cobalt and longer duration in iron toner (left below).

cobalt 1:50 minutes - iron 3 minutes

For comparison a print directly toned to blue in MT7

You have the option to tone first in selenium or sulphur. Here an example for a combination of thiourea-, cobalt- and iron toner.

If you use sulphur to only reach the highlights and tone comparably long in cobalt, the iron toner can only intensify the cobalt image.

MT3 Vario-Sulphur Toner
bleach 1+80 for 30 seconds
thiourea toner in configuration A yellow

cobalt toner for 2½ minutes

iron toner for 1 minute

Cobalt toning followed by iron toning

Irrespective of the paper you use, cobalt toning is not only unspectacular in terms of colour but also results in light and dull prints.

Fomabrom toned in cobalt toner for 3 min.

same as to the left, plus toned in ferric sulphate for 3 minutes

Ilford MGW toned in cobalt toner for 3 min

same as to the left, plus toned in ferric sulphate for 3 minutes

Toning in selenium for a short time (see below) not only shifts the colour of the shadows, as was to be expected. With prior selenium toning, the darker areas show at least the same density already after 2 minutes of iron toning as they would have after 3 minutes of toning only in iron. This means you can stop now if you want the colour of the highlights to stand out. If you went on toning, the highlights would also shift to a bluer tone and the shadows would become too dense. If you desire a continuous blue tone without any whiff of green, you have to print a bit lighter.

Fomabrom selenium 1+10 1min and cobalt 3min

plus toned in ferric sulphate for 3 minutes

Polywarmtone toned in cobalt for 2 min.

plus toned in ferric sulphate for 3 minutes and then treated in
an ammonia bath for 1 minute to reduce the colour saturation
of the mid tones

If you want the result to be less intense in colour, you can decrease the duration of toning in cobalt and further dilute the iron toner solution.

If you want to achieve hues between magenta and violet, tone in iron for only a short time. With increased duration in iron the print turns bluer.

Infra red picture on Efke IR820c

ADOX Easy Print VC PE in SE6 Blue

top left: cobalt toner for 60 seconds

top right: iron toner for 30 seconds

left: iron toner for 90 seconds

Kentmere Fine Print VC
developed in SE6 Blue

This neutral to cold tone emulsion can be toned to intensive colours, if you keep the print in cobalt toner for between 2 to 4 minutes and prepare the iron toner a bit stronger or with a slightly increased content of acid.

Ilford MG Warmtone
right the typical colour of cobalt toning
left with additional iron toning

Toning of all sorts can also be done after intermediate drying. For some toning methods it is an advantage to dry the print in between, because the gelatine becomes sturdier.

If you dry on a strainer, do not place the print with the emulsion side down, as commonly done. In all following toning methods with bleach, this could result in an imprint of the strainer ruining the print. Do not use an automated dryer either. In most cases, its linens are not entirely clean.

Selen vor Kobalt

Polywarmton toned in selenium 1+10 for 45 seconds
and then in cobalt

plus ferric sulphate for 3 minutes

If you first tone in selenium, the loss of density in cobalt toner is low. Fortes warmtone emulsions react quickly to selenium. So either tone only for a short time or use a dilution of less than 1+10. The iron toner will not find much untoned silver, so that the blueing effect is small. Surprisingly, the iron toner only increases the shadows that have already been darkened by selenium. Even if you tone for 3 minutes, the highlights do not adapt any blue, but appear in a bright reddish-yellow tone.

Lith and polychrome development

The shape of the silver produced by lith development or two bath development with lith as first developer is different in highlights and shadows in terms of size and structure. As a result, split toning - meaning a colour separation of groups of tone values - can be achieved easier this way than with conventional development.

Select VC (PW15)
two bath development in lith and siena

toned in cobalt for 1½ minutes and in ferric sulphate for 30 seconds

Fomatone MG 132
two bath development in lith and siena

toned in cobalt for 1:30 minutes and in
ferric sulphate for 30 seconds

Cobalt and ammonia ferric citrate (MT7 plus bleach)

polychrome print (lith + siena) on Select VC

cobalt and blue toner MT7
ammonia ferric citrate / ferricyanide toner

If you first tone in cobalt and then in a normal configuration of MT7 Iron Toner (meaning with bleach substance ferricyanide), the effect on the range of densities is quite different from all other iron toning without bleach mentioned so far. Depending on the intensity of cobalt toning, if you tone in iron for a longer duration a violet to magenta tone appears only in the mid tones. The highlights turn blue-grey. The shadows first show a deep blue and shift to blue- green only later. The densities continuously decrease until even the deepest blacks have switched to a blue green tone. In contrast to all toning so far with iron as second toner, the shadow densities do not increase but decrease. You can make use of this characteristic when toning polychrome prints. Polychrome prints have a high silver density in the shadows. Lith black is a lot more resistant towards the toner than the adjacent slightly lighter shadow zones. If you miss the right moment to stop the toning process, the zone 1 black will also turn green at some point.

Cobalt + MT7 Iron Blue

same as to the left plus copper toner

Working with a direct iron toner naturally also brings us yellowing and with it the necessity to clear before the final rinse. This is only one more step on top of all the effort that has been put into the image anyway.

The image whites, including the unexposed image border, should appear as white as before the ordeal of toning. Not every paper can achieve this. A little diminishing of the whites may be tolerable, but spotting on the image borders is not.

Normally a 2% solution of sodium chloride is enough to remove these ferric salts. There is a powder for the preparation of a clearing bath included in delivery of both MT7 and MT12 toners. Apart from sodium chloride, it contains a citrate to lessen the acidity of the solution. As an alternative a common salt solution (without iodine) is sufficient.

Select VC

Using cobalt toner for only 45 seconds gives a delicate tone to the highlights appropriate for this picture.

MT7 in a slightly stronger solution for 20 to 30 seconds only tones the mid tones.

The whites were cleared by bathing the print in a common salt solution for two minutes. To avoid a reduction of the green densities in alkaline tap water, the rinse water in the dish was slightly acidified and renewed a couple of times for rinsing. (Some drops of acetic or citric acid were added to the water.)

This print was toned slightly longer:
cobalt for 1½ minutes and MT7 for 45 seconds

The darkest shadow zone that still shows delineation - just below the sill - is dark green. The following zones are bluish and the highlights appear with little density and colour.

Clearing the image whites was not entirely successful. A delicate yellowing is still visible. To make this more obvious, I increased the saturation of the image border in Photoshop by 50%.