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Indirect iron toning
Generally speaking, all references state toner and bleach together. However, it is not always mandatory to use this combination.

Toner substances:
Fferric sulphate, Ferrous sulphate, Ammonia ferric sulphate, Ammonia ferric citrate, Ferric oxalate

Acids:
Hydrochloric acid, Sulphuric acid, Nitric acid, Citric acid, Acetic acid, Oxalic acid, Tartaric acid

Bleach:
Potassium ferricyanide (red prussiate of potash, potassium ferrocyanide) with or without addition of: sodium carbonate, ammonia, potassium oxalate


Die interessantesten Rezepturen für den Selbstansatz im Überblick:

Bleach #1 - 2-10% solution of potassium ferricyanide
Bleach #2 - 40g of potassium ferricyanide, 40g of potassium oxalate on 1 litre of water
Bleach #3 - 20g of potassium ferricyanide, 100ml of a 10% solution of ammonia on 1 litre of water

All three bleach baths work quickly and sweepingly with warmtone papers. Use bleach #2 or #3 for pure bromide silver emulsions and mixed emulsions.

Important! Rinse thoroughly after bleach. It is not necessarily enough to rinse only until the yellow cast has vanished. Residue of ferricyanide reacts with toner substances, resulting in a blue dye (see also direct toning) that can affect the print surface and drastically shortens the durability of the toner.

Toner #1 according to Agfa
800ml distilled water
20g ferric oxalate (toxic and expensive)
10g oxalic acid
10g potassium bromide
Add distilled water to make 1 litre of solution

Toner #2 according to Eder
700ml distilled water
1,8g or 18ml of 10% solution of ferric sulphate
(alternative: 175ml of a 10% solution of ammonia ferric sulphate)
40ml of a 15% solution of hydrochloric acid
9g or 90ml of a 10% solution of potassium bromide

Toner #3 according to Somerville
800ml distilled water
20g of ferrous sulphate
100ml of a 10% solution of hydrochloric acid
Add distilled water to make 1 litre of solution

All combinations of these bleach baths and toners result in green-blue or pure blue image colours. The outcome can vary in tint and densities. With a number of papers some combinations can result in an unpleasant yellow dyeing of the highlights. In such cases after-treatment in diluted sulphuric, citric or hydrochloric acid can be the remedy. The gelatine is decolorized but the image colour is preserved. Using 2-5 ml of a 15-20% solution of acid on 100ml of water, the highlights will clear after 2 to 3 minutes. If you want to change the green-blue tone to a pure blue or delft-blue, give the print an after-treatment in a weak alkaline bath (borax, sodium carbonate, ammonia).




Fomabrom Variant III
bleach #1 (2% solution) 2½ min
toner #1 30 sec




dyeing of the gelatine cleared
in a weak sulphuric solution



Compared to the untoned print the densities of the shadows are decreased. The contrast of the print is not satisfying.

Depending on the duration, after-treatment in a weak ammonia solution changes the colour to pure blue or magenta. At first, the densities of the black areas increase. Only after longer times of treatment - starting from the highlights - the print loses saturation and density. After around 30 seconds the colour has a strong tint towards red. If you stopped the process now, the colour would shift a bit back to its original tone. If you want the print to appear as in the photo to the left 50-60 seconds of treatment is necessary.

 


Fomabrom Variant III
bleach #1 2½ min
toner #2a 30 sec

With this toner you will also get a yellow tint on both sides of the print. to the left: print cleared in sulphuric acid.

The colour of the highlights does not differ much from the example above. All in all toning resulted in a darker image with a better contrast. The surface of the print is more lacklustre in the toned areas than on the white image border.



Bleach #2 and #3 in combination with toners #1, #2 and #3 show an as strong diminishing of the image whites. Note here, that with a decreased content of iron-salt the transformation of silver to dye is incomplete. This means, the less ferric salt in the solution the more will the prints darken.





Fomabrom Variant III
bleach #2 30 sec
toner #3 ferrous sulphate 30sec

Colour after drying: blue-green
After a couple of hours of exposure to light the print darkens and the colour shifts to a purer blue.




Somerville-Toner
(bleach #3 and toner #3)

If you bleach this paper (!) for only 30 seconds to preserve the shadows in an as deep black tone as possible (similar to sulphur toning), you get an unexpected - and here undesired - effect when toning in ferric sulphate. The shadows increase with a completely dull surface. On the transition to the mid tones you get a solarisation-effect and the highlights tone blue with a glossy surface.

A check-up in a different bleach and toner combination results in the expected effect.

bleach #2 30 sec
toner #2 30 sec

Using the same times of treatment as above, but in a different combination of bleach and toner, everything works as expected.

After bleaching for 30 seconds, the deep shadows remain. Toning is spotless, the brilliance is preserved and the white image border is only slightly yellow. A short bath in water that is slightly charged with citric acid will clear the whites.


According to my own test results, the Somerville-Formulation does not seem to be suitable for just any paper. Unfortunately, the writings of Somerville are not to my disposal, but they say that his publications to this topic exclusively refer to bromide silver papers. According to name Fomabrom is such a paper, but I cannot say why it does not react accordingly. When I compare its surface to that of other papers - explicitly after maltreating the gelatine with long developing times or in highly alkaline toners - it is less glossy. This is a hint to weak hardening of the gelatine, which would also explain some problems when toning. Surprisingly, the warm-toned sibling from the same manufacturer has no problems hardening at all. Even if the gelatine is treated in extreme conditions, the surface of Fomatone MG 131 emerges in a fine gloss.





Fotokemika Variocon
Adox Fine Print Vario Classic
Maco Multibrom

The neutral tone VC-bromide silver emulsion of Fotokemika gives good toning results with all formulations. It also darkens down quite a lot.

The Somerville Toner
(bleach #3 and toner#3)
right: bleached for 90 seconds
left: bleached for 30 seconds
both toned for 60 seconds
left: the colour just after drying.
further down below: the change after exposure to light.




Kentmere Fineprint VC
bleach #2 bleached almost completely
toner #2a ferric sulphate

Here as well, the print darkens a little bit afterwards. Colour saturation of the highlights decreases and the shadows become deeper.


Agfa MCC
bleach #2 for 60 seconds

Toner
left #2a ferric sulphate
right #2b ammonia ferric sulphate

Top right: the content of acid is as high as specified in the instructions. Below right: acid is reduced to half. Apparently, you need a particular content of acid to fully depict high densities. An increase of the duration of toning does not change the result. The deep shadows are not reached by the toner.





It is not so important, which of the two iron-salt solutions you choose. Using the same content of acid, ferric sulphate tones a little bit more greenish than ammonia ferric sulphate.


 
Exposed to light, warmtone papers darken down a lot.
The test on Select Ivory (PW17) - in bleach #2

left: toned in ferrous sulphate
right: toned in ammonia ferric sulphate

The light blue stripes show the colour right after drying. These parts were covered while the test strip was exposed to direct sunlight for 3 hours.

Bromide silver paper also darkens down. The tone, which was originally bright blue and too light compared to the untoned print, turns considerably darker. Colour intensity decreases.





Kentmere Kentona
This paper also shows its definite colours and densities only after longer exposure to daylight.

Left: The scan just after drying.

Below left: After one hour exposure to direct sunlight.

Below right: Different combinations of bleach and toner do not lead to a substantially different effect. Only the tint changes slightly.



bleach #1 (2% 90sec) toner #1


bleach #2 (60sec) toner #1


Of course, bleach #1 (pure ferricyanide) in a 2% solution works slower than the strong solutions of bleach #2 and #3. Irrespective of the concentration and with sufficient rinsing before toning, the use of bleach #1 in combination with any toner results in a slight yellowing of the whites in the picture. Apparently, adding potassium oxalate (#2) or ammonia (#3) to the bleach promotes clear whites.





For comparison: the effect of my direct toner MT7.

The range of contrast is higher. With the same density in the highlights, the shadows are darker than with indirect toning and also darker than the untoned print.

The Dmax reading supports this visual impression.
Kentmere Kentona in SE4 NEUTRAL 2min

Dmax before drying 2.15 logD
Bleach #1 / toner #1 1.93 logD
Bleach #2 / toner #1 1.99 logD
MT7 (90sec) 2.44 logD



Ilford MGIV tones light blue with reduced density in the shadows. It only adopts a less intense, but very pleasant colour when darkened down by exposure to light. The mid tones appear clear blue, without any trace of green and the highlights show a whiff of magenta.

Bleach #2
90 seconds of bleaching reaches only as far as the mid tones. After toning, only the bleached areas show a light blue tone. If the print is not thoroughly rinsed immediately, you can observe in the first rinse water that the toning process increases in the shadow areas that have only been slightly bleached - especially when the rinse water is slightly acidic.



Conclusion

Indirect iron toning only leads to reproducible results, if you know the characteristics of the material that you use and standardize the complete process. Any deflection from your field-tested work-flow can lead to disagreeable surprises. It may seem to be an advantage over direct iron toning that the working solutions have an almost unlimited shelf-life. However, with the effort that is put in either way, the expenses of the solutions are comparably small.

You may notice that more expensive, high-quality papers can have advantages over cheaper alternatives. Only the inexpensive Kentmere Fine Print can keep up with MCC and the papers of Ilford in terms of quality of the result of toning. If you are not after an extra satisfaction by creating your own formulations you are better off using the ready made Iron-toner MT7. If used according to instructions, you will not have to fear problems with darkening, staining and loss of gloss of the image surface.