The Van Dyke Process

Another of the direct copying processes that has a relatively simple chemical basis, is neither complicated nor hard work and is possible to carry out easily, even under simple conditions, is known in the English literature as Van Dyke Brownprint or Sepiaprint (sometimes just Van Dyke or Brownprint). So far there is no Czech equivalent, though in this series we have used the term Sepiový tisk Van Dyke.

In principle it is among copying processes based on the sensitivity of ferrous salts to light. The sensitising solution contains iron ammonium citrate, silver nitrate and tartaric acid. With UV radiation iron(III) ions (Fe3+) are reduced to iron(II) ions (Fe2+), which in turn reduce silver ions (Ag+) to metallic silver (Ag) forming the picture. The basic principle has already been described by John Hershel in connection with argentotype, cyanotype and chrysotype in 1842, but was not elaborated in detail until Dr. Nicol, who had it patented as Callitype in 1889.

The principle of the Van Dyke process is similar to Callitype and it is even often considered as one of the Callitype methods. Van Dyke is, however, simpler and easier to carry out, since instead of iron ammonium citrate Callitype uses a more expensive and highly sensitive substance – ferric oxalate and after exposure it requires developing in a specially prepared bath.

The Van Dyke process is very popular among those interested in historical photographic techniques abroad. It is relatively quick, cheap and during work there is no chance that we will meet with so many unforeseen problems as with other processes.

During sensitising only one layer is applied to the paper. The sensitising solution is simple and very durable. The process requires a minimum of operations. Negatives need not have as high contrast as, for example, with the salt paper process. Quite short exposure is sufficient. If we do not require gallery quality in our pictures, we needn’t use any special paper. We can apply the sensitising solution to other materials, such as fabric or wood. The durability of the picture is the same as for the salt paper process – our pictures may well even survive not only us, but also our children.

The greatest advantage is the minimum operation cost.

Whilst the set for platinotype is offered by Bostick-Sullivan in the USA for $ 144 (containing 25 ml sensitising solution, thus sufficing for 25 copies of 4 x 5 inch format) it offers the set for Van Dyke for $ 22 (containing 100 ml sensitising solution, thus sufficing for 100 copies of 4 x 5 inch format).

If we prepare solutions for Van Dyke from individual chemicals ourselves, which is quite simple, we can purchase them for about a fifth or tenth of that price.

If we develop the Van Dyke process, we will be able to achieve results of a very similar character to much more expensive and complex platinotype. As in platinotype, the picture is not in binding agent – thus on a sensitive layer on the paper’s surface, but anchored directly between the paper fibres. If, despite this, we still want to try platinoprints – for example, because of their fineness, value and durability, we can subsequently tone pictures made with the Van Dyke process with potassium chloroplatinite, whereby we achieve pictures almost identical to those from platinotype, for about half or a quarter of the price. In comparison to platinotype we also have the advantage that we can only tone selected and really good pictures. We can tone in the same way with auric (gold) chloride.

Sensitising solution

We add solution 1 to solution 2 and mix well, then we add solution 3. We should acquire about 100 ml of sensitising solution, which should be enough for about 100 copies of 9x13 cm.

We use distilled water here because the chlorides contained in tap water would precipitate silver nitrate to silver chloride and the solution will cloud.

Iron ammonium citrate exists in both brown and green form. We use green here because it's more effective.

Tartaric acid is a raw food material and we can buy it in a drugstore.

We will have to get silver nitrate in a shop selling chemicals (priced up to ca. CZK 10 a gram).

We must be very careful when working with silver nitrate and ready sensitising solution. If the sensitizer touches our skin, the contact point will turn black and nothing will wash it off. We should definitely protect the eyes. The literature states that getting silver nitrate in the eyes can even cause blindness.

It is best to use the ready solution the next day, as it needs time to ripen. We store the sensitizer in the dark, if possible in a full bottle. A dropper bottle from the chemist’s is a good idea. You may also be able to get plastic dropper bottles of 25, 50 or 100 ml.

In a well closed bottle stored in the cool and dark the sensitizer can last several months or longer. We tried a solution about one year old, stored at room temperature in a half-filled bottle. The picture quality was indistinguishable from a picture using a new solution (Fig. 2).

Paper

The appearance of the picture is very dependent on the type of paper used. The best results we achieved were with paper supplied by EMBA for archiving photographic material (see PhotoArt No. 5). Also good was Italian 100 % cotton Fabriano Artistico, which was slightly less sized and had a slightly more yellow tinge.

Only slightly less good was paper labelled as graphically glazed from Excudit.

We also had good results with handmade paper produced for art purposes. However, it was not sized sufficiently, during application with sensitizer it soaked up quickly, so it was necessary to apply more, which was manifested after exposure as grey stains from excess sensitizer. We tried subsequently sizing with a gelatine solution, the results were better, but the colour was a bit cooler. Subsequent sizing is possible, but if we don't have any leftover paper and we buy new paper, it is better to buy paper which needs no sizing.

We tried working with drawing card in rolls of 1.5 m width (also known as cartridge paper). The picture on them had a little lower contrast, a cooler shade, but still quite acceptable for less demanding requirements.

A picture on regular drawing board also had less contrast (manufactured by Krkonošské papírny – KRNAP), again still acceptable for less demanding requirements.

From tests of various types of paper we can conclude that for Van Dyke almost any paper is possible (see Fig. 1). If we require quality comparable with pictures on modern bromide paper, we will need to use the highest quality paper we can find. We found the best to be “Fotopapír” made by EMBA (Paseky nad Jizerou).

It is possible to sensitise natural fabrics similarly to paper, provided they are made of 100 % plant fibres, for example, cotton or flax. Pictures can be copied onto a cotton t-shirt and the picture should resist normal washing in a machine.

Paper sensitising

We take the smooth side of the paper and cut out a format several centimetres larger than the negative which we intend to copy.

We attach it with pegs or stick it with sellotape onto the glass and mark the corners with a pencil. We use a flat brush with soft fibres (e.g. goat hair) and no metal parts, best a hake brush. We wet the brush in distilled water and dry well with unbleached toilet paper (this is better than a kitchen towel, which is usually bleached with additives).

We work under normal tungsten light, with a 60 W bulb at a distance of about 3 metres.

We only measure out about 1 ml of the sensitizer into a small glass or beaker and wet the brush in it. We coat the marked area first with vertical brushstrokes and then we cover the whole area with horizontal strokes. The brush must be wet only enough so as not to leave areas with accumulated liquid. We can observe the uniformity of application by tilting under the light. If areas with accumulated liquid still form, we wipe them off with toilet paper.

Important is correct sizing of the paper. Paper is suitably sized when all the liquid soaks after quick application and it is damp in the light. If it is sized too little, the solution is sucked up too quickly, which leads us to further application and grey patches visible just after exposure occur. In the course of the Van Dyke process these excess areas usually disappear, though their tracks remain in the ready pictures. If paper is sized too much, the solution is absorbed slowly and isn’t well anchored between the paper fibres.

If, when tilting the paper, we see that the glaze of the paper is uniform without dry patches or, conversely, we see places with excess solution, we leave the paper in the horizontal position to dry for a few minutes. We dry naturally (best in the dark) by hanging on a clothes line. For faster drying we can use the air flow (cold) from a hairdryer (under weak bulb light).

Exposure

The length of exposure for the Van Dyke process is about 30 to 50 % shorter than for the salt paper process. We expose outside in the open air (not through a window, since glass retains UV radiation to which the paper is sensitive). If we have negatives with less contrast, it’s better to expose in the shade or under an overcast sky, negatives with higher contrast can be copied in the sunshine. When the sky is overcast the exposure time can be up to half an hour, a few minutes can suffice in direct sunlight. It’s good to have our own source of UV radiation, which can give us good results independent of the weather.

If we have a segmented copying frame, we can keep an eye on the process of copying by opening up one part of it. Of course, for that we have to take it inside, into a room with weak electrical lighting.

It is important to learn how to estimate the density to which it is necessary to copy a picture. A correctly copied picture is weaker than the ready copy will be. In Figure 3 you can see how the appearance changes in the course of processing. The lower figure shows the picture just after exposure, the higher figure the picture after drying. You can see how chiefly the density in shadows has increased after processing and drying. For determination of the required period of exposure the light areas are decisive. Density in the light areas only increases slightly after processing (in particular, the colour of the picture clearly changes). We copy long enough for the lightest parts, which we want to be seen clearly in the ready picture, to be noticeable in the emerging picture.

If we know how to weaken with potassium ferricyanide (see Photoart No. 7), we can get perfect pictures even from slightly overexposed copies. In Figure 4 we see that, aside from lightening the picture, its tone also partially changes – the weakened picture is toned more to yellow.

Development in water

An advantage of the Van Dyke process is that no special developing bath is required, but processing occurs in ordinary water. 1 to 2 minutes is enough, but we should change the water at least twice. After submerging in water the shadow areas are significantly intensified, the picture has a markedly red tinge. In the course of developing a large part of the unused silver nitrate is washed from the paper. We can see how clusters of whitish material are released from the picture into water – this is silver chloride emerging from silver nitrate by reaction with chlorides contained in tap water. The residue of unused silver nitrate is removed by subsequent fixing in thiosulphate.

In the developing water ferrous salts from the sensitizer are also washed from the paper. From this point of view the quality of water used in the whole process is important. The water shouldn't be alkaline, since ferric hydroxide can occur in the paper, which is not possible to completely wash out and reduces the durability of the picture. Some sources therefore recommend acidifying the developing water with a teaspoon of citric acid. Here at the National Technical Museum we have tap water with pH above 8. We have used it without modification for developing and washing out, and so far we have observed no adverse effects. We even tried acidifying the developing water with citric acid, but we observed no changes. Pictures made a year ago show no changes from their original appearance.

Fixing

After developing it is necessary to fix the picture in a solution of sodium thiosulphate. This removes the remainder of unused silver salts. Almost immediately after immersing the copy in the fixing bath, the reddish tinge of the picture changes to brown, which significantly intensifies the picture (particularly in the shadows) and it looks very good. After about 20 seconds of fixing it begins to pale again and after about 2 minutes it is already significantly weaker.

The problem of weakening of the picture during fixing is specific to the Van Dyke process and can be resolved in two ways. The first method is based on the addition of about 2g sodium carbonate to the fixing bath, which suppresses the weakening of the picture. With the other method a weaker fixing bath is used and fixing occurs for the necessary time only (see Figure 5).

Usually a 3 % solution of sodium thiosulphate is recommended as a fixing bath (thus 30 g thiosulphate per litre) with the addition of 2 g sodium carbonate, with fixing of about 3 minutes. However, even adding sodium carbonate does not prevent a certain weakening of the picture. Another disadvantage is that sodium carbonate makes the bath alkaline, which complicates washing out residual ferrous salts from the paper.

With the second method, where we fixed only for the necessary time, the picture does maintain its original freshness, but the question is whether such a short time is enough to dissolve the remaining silver salts. With imperfect fixing the picture would quickly degrade under light.

Since picture durability is a principle matter, we made a comparison at the National Technical Museum of both methods of fixing for the same copy, which we tore into two parts after developing in water. The first part was fixed in a 3 % solution of thiosulphate for 2 minutes, the second part for only 30 seconds. After drying, we again joined the two parts together, stuck them outside on the window and subjected them to about half a year of daylight, including direct sunlight. After half a year's exposure, as could be expected, the picture was significantly faded, but both parts faded exactly the same.

We consider this sufficient proof that fixing for 30 seconds in 3 % thiosulphate is enough (see Fig. 6).

Our recommendation is thus: fixing in a 3% solution of sodium thiosulphate (30 g per litre) for 30 seconds.

Sodium thiosulphate comes as large translucent crystals and the easiest way to get them is to take them from a normal two-part commercial acidic fixer (it consists of sodium thiosulphate – the larger part - and sodium pyrosulphite – the smaller part).

Washing out

The fixer residue should be removed by final washing. We wash it in the largest possible tub, moving the copy intensively and changing the water about every 5 minutes. It’s better not to use circulatory washers intended for normal baryta paper, since our papers lack a classical strengthening sensitive layer and are delicate enough to rip. Furthermore, when washing with running water, air bubbles can form on the surface of the picture preventing thorough washing out.

Thicker papers require longer washing out than thinner ones, since the thirosulphate residue is soaked deeper into the paper. Board (paper stock weight of about 200 – 300 g/m2) should be washed out for about 30 minutes; thin paper requires 15 – 20 minutes. If we are test developing and don’t need longer durability, 5 minutes washing out is enough.

Washing out can be shortened by a 1% sodium sulphite bath. After fixing, we briefly rinse the copy and then dip it for about 3 minutes into the sulphite solution, occasionally moving the picture. Washing out can be thus shortened by half.

Drying

We dry the pictures in the normal way, hung with laundry pegs on a line. Pictures on card will not curl and it is sufficient to hang them on the line by just one corner. It has the advantage that the water will run down from the surface to opposite corner and form a drop that we can easily soak up.

Thinner papers should be hung by two corners. After drying they could be slightly buckled. We stack them and weight them down, for example, with several books. They are quickly pressed out. Since they have no sensitive layer (the picture is actually anchored in the paper fibres), they have no reason to curl up and, if well pressed out, they will remain straight forever.

After complete drying the appearance of the picture changes again – it significantly browns, strengthens and becomes more marked. We will like our pictures only after final drying.

Toning

We have already mentioned that pictures can be toned. Most often they are toned with auric chloride or potassium chloroplatinite either alone or mixed with palladium dichloride. The tone of the picture differs based on the recipe used; mostly they are yellowish or bluish variations of brown.

An advantage of toning is that it significantly increases the durability of the picture. A disadvantage is the cost of the process – salts of gold, platinum and palladium are quite expensive. Furthermore, unless we have the possibility of buying ready solutions abroad (e.g. made by Bostick-Sullivan in the USA), it will be difficult to find these substances.

Toning is possible prior to fixing or after fixing. Both methods have their advantages and disadvantages.

The Van Dyke process compared with other alternative copying methods. Creative workshops at the National Technical Museum in Prague.

Anyone who has tried the salt paper process or another direct copying process and then tries the Van Dyke process will be pleasantly surprised by the smooth course of work. For that reason it can be recommended as one of the first historical photographic techniques to try. We will gain experiences from it which will help us later with work with other, more complex and costly techniques. If we master the basic procedures of one alternative copying process, work with each further process will be easier – we will save time, efforts and money.

These facts led us at the National Technical Museum in Prague to plan to hold one-day creative workshops on the Van Dyke process for the public (starting October 2007, notice will be given on the National Technical Museum website). Since we are preparing the necessary baths ourselves, work will not be expensive and we can equip participants with the required baths so they can continue themselves at home.