Wolfgang Moersch Photochemie
Am Heideberg 48
50354 Hürth

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Lesson 2: From application to developement
Mixing and applying the sensitized solution

Iron(III) oxalate (ferric salt) and silver nitrate are mixed in equal parts inside a small cup. Care should be given that the used cup is dry. Even little amounts of tab water can react with silver nitrate. The solution becomes useless if it turns cloudy. Eight up to ten drops of both solutions are sufficient for coating (with a glass-stick) an area of 8x10 inches. Opposite to platinum-prints a stock of coated sheets can be prepared, staying good for a few days.

Not all paper sorts witch giving good results with platinotypes, are suitable for Kallitypes. The process depends highly on the quality of the used printing paper. I use exclusively the brand Arches Platin. The 300g heavy paper made of cotton does not only makes handling easier and the finished print brightens the eye it also gives a good feel. It has the “right” sizing for all noble printing techniques, its coating does not “swim away”, iron salts dissolve faster inside clearing baths, the long-fibre cotton makes washing easier and an out-bleaching during each working step is not expected.

Brush or a glass-stick ?

At coatings with a brush the layer is thicker, the print seems more powerful. By coatings with a glass-stick the layer is more homogenous, thinner, the resolution and sharpness higher.

With a brush:

The marked area has to be brushed quickly. The movements should be relaxed, without great pressure and the solution be spread richly with crosswise movement. The strikes which are still visible at the beginning should be dispersed with another, spreading brush (preferably badger hair) in order to get an more even result. This is done by moving the tip of the brush upon the layer, no difference the direction but in a very quick manner. All kinds of pressure has to be avoided thus this will only push the solution away instead of dispersing it. The strikes will not be disturbingly visible upon structured motives but every single mistake will occur on homogenous picture areas. The print below shows clearly the result if homogenising with a spreading brush is left out.

With a glass-stick:

The glass-stick is to be placed on paper and the emulsion be dropped with a pipette along the glass-stick up to the desired length. Streaks upon the layer are normal. If there is enough solution, it can be spread with pressure upon the stick to the desired lenght. Following that, the stick is pulled downwards, then set behind the collected emulsion and pushed upwards to the point of begin. Finally, after two, maximum four times the emulsion should be spreaded evenly. Surplus parts of the emulsion at the endings should be removed with paper towel etc. If it is left, it could be absorbed up to the parts where the negative is replaced.

Wrong application


If the final picture shall not have a brushed frame the negative must be masked.

If the film size is larger than the picture, the borders of the negative can be blackened by exposure. This is done by covering the picture area after exposure with a black cardboard, pushing the masking slides aside and exposing the borders directly from above (e.g enlarger light, without a negative inside).

An easier way is covering with light-proof, adhesive bands or preparing a mask made of black folio, black cardboard or overexposed PE/RC photographic paper. The pressure produced with a glass-plate in this method is not sufficient enough to build up a real contact between paper and the negative, so that unsharpness will occur. Only vacuum-easels pull the sandwich tightly upon the paper.

For judging the clearing, masking is helpful at first trials but it is also sufficient if a small corner of the emulsion is covered up during exposure. The light sensitive substance (here ferric oxalate) has to be dissolved completely in order to assure long-time durability. As long as the unexposed corners have a yellowish tone, there is still ferric salt inside the paper. At the beginning of development the emulsion-corners are still visible. The reason for a developing time of four minutes or more is not for increasing the density but for dissolving the ferric salt. This tone will finally disappear inside a clearing bath of citric-acid and the unused silver inside the fixing bath.

A yellow coloured corner is a sign of ferric salt residue. If clearing is not complete after four to six minutes, the chosen paper is not suitable for this process. The corners will turn grey if the room was to bright during positioning the printing negative or the use of a permeable material for masking.

This example shows how the paper should look after processing. The small sign above left is a pencil mark made on each corner showing the borders of application for the sensitised solution. These marks can easily be erased afterwards if a soft pencil was used.

Self defined masking corners

Whenever a black frame without the irregular patterns of a brush or glass-stick is desired the negative should be placed inside a black mask.

An unsharp corner occurs if the mask is placed two or three millimetres upon a negative. Because of the broken light, a slight tone can cover the complete application area. This can be removed after fixing by using a reducer (better bleaching and removing inside the fixing bath). The bleacher has to be diluted at 1+20 and applied with a cotton-wool ball. If the print has been left to drip off before, the bleacher cannot penetrate the paper within the 20-30 seconds of working time and destroy it. During such procedures, I always grab a long side only and then the short, the print lying on an even surface (e.g. shelves of an archival washer etc.) which is kept slightly tilted in order to let the solution flow downwards.

Photographer: Albert Renger-Patzsch
Toning: MT6 Nelson Gold after fixing

Contrast control

If the contrast range of a negative is too low the print will appear weak or with overexposing too dark and undifferentiated. In such cases the developer can be made “crisper” by adding Dichromate.

This negative has been prepared for the gum dichromate process thus gentle and without high tone density. The proof was exposed for two minutes from a distance of 12 cm (UV-Light) and cut into two before development. The part on the left was developed in sodium citrate without additives, the right one in the same developer by adding 40 drops of sodium-dichromate (50%) on a litre.

It is visible that highlights and middle tones get brighter. The shades stay unaffected at this amount of chromate if exposure time is increased accordingly. At the example below, exposure is correct for the developer containing chromate. As for the developer without chromate, exposure time has to be reduced by 50%. Even if the density is being checked with a densitometer, negatives can be too thin. A perfect negative to process is advisable but controlling the contrast with chromate inside the developer makes more sense. It is also advisable to prepare 2-4 developer baths containing 0,10,20,40 drops of chromate for a litre and per printing session if the negatives have different contrast ranges.

Photographer: Matthias Stalter

Even polanegatives can be used if they have enough density. If the exposure is made for obtaining the best possible density for the negative (not for the positive), 2-3 drops of dichromate onto 100ml if citrate-developer are sufficient.

If an untoned Kallitype happened to be too dark because of overexposure, it can be reduced just like any other silver gelatine print.

In order to control the effect of the reducer, the process is made inside a weak hexacyano solution. For this reason, I have diluted my reducer concentrate at 1+100 and processed by sight. After 20 seconds a quick washing and fixing completed the process. Fixing afterwards for 30-60 seconds is sufficient.

Reducers based upon hexacyanoferrate (potassiumferricyanide) first influence the highlights followed by middle tones and finally the shades. Therefore there is enough time for interrupting the process before the reducer reaches the shades. This reduced print has no difference in tone and maximum density if compared with a perfect exposed one.

There is only one way if a overdeveloped negative on which highlights are clear and shades too thin shall be used for printing. It must be exposed onto the highlights resulting in a “heavy” print with covered shades.

At the example above using a reducer would not give us to the expected result because the highlights would become undefined until the shades get affected. In such a case, the print, after complete washing, is reduced from the highlights to the middle tones and then protected by a sulphur toning. After drying up, the print will be visibly brighter then before.

The picture tone always changes into a yellowish-brown whenever a sulphur toning is used after a strong reducer. The most economical toner is a solution of thiourea with high alkalinity.

If shades still remain too heavy it has to be reduced again. Sulphur-silver will not be influenced by the reducer so that only picture areas containing metallic-silver will be affected. The time for using a reducer has to be measured in a such way that dense shades remain unchanged. Thus, in order to have enough time for controlling, the reducer has to be diluted at 1+500.

Finally the print will be fixed, washed and dried up.