Paper sensitising

Options for negative preparation

With historical copying processes, for which we prepare sensitive papers ourselves, we copy the negative by contact. The resulting picture is thus precisely as large as the original negative. Use of an enlarger is not possible due to the very low sensitivity.

An original negative made by a direct photographic camera

Formerly photographs were commonly made on glass plates of 13 x 18 or 18 x 24 cm format and the developed negatives were used directly for copying the positive. These days few now photograph with those formats. Many photographers usually work on 6 x 9 cm or 9 x 12 cm formats. If we do not need large pictures, we can work sufficiently with 6 x 9 cm negatives. Small pictures are quite nice and if we are not holding an exhibition in a gallery, they are often good enough. The use of an original negative for copying is the purist method and the most valued method historically and for collectors.

If we want to use an original negative directly for a historical copying technique, we will have to develop at a much higher contrast than is sufficient for enlargement for today’s photographic paper of normal gradation. We need a negative which we would enlarge on paper of soft or extra soft gradation. Since each of the historical copying techniques gives a slightly different contrast, we recommend working with only one of them at a time and adapting them to developing the negative.

Enlarged duplicate negative

If we prepare the negative for contact copying separately, it has several advantages. Above all, we will have the option of choosing a motif from our archive which we like and which suits the selected technique. Every photographer knows that a good shot is achieved often after many attempts and trips to the subject. In an archive acquired after years of work with film we can probably find a more suitable shot than by going once or twice into the field with a large technical camera. If the original negative is on material of low to medium sensitivity, if it is overexposed or overdeveloped, we need not worry that its structure will be obvious at a format up to 18 x 24 cm. In the final picture the structure of the paper used and the colour tonality of the picture will be more significant.

Procedure with cut film

The usual method of preparation of a duplicate negative is two-stage. The original negative may be of any size. In the first step we make a transparency from it. For this purpose it is best to use primed orthochromatic cut film which can be worked with in the darkroom under red light, for example Ilford Ortho Plus. To achieve the contrast required for our purposes it can be developed with normal positive developer (2 to 4 minutes) under red light. Lower contrast is achieved by developing in normal negative developer, for example ID 11 or Microphen. Cut film is supplied in standard formats from 9 x 12 cm.

We can create a transparency either by contact from the original negative or we enlarge the original negative with an enlarger to the resulting size. In the first case we acquire a transparency of the size of the original negative which we enlarge in the second stage on the same material to the resulting required size of the final negative. In the second case, when we have a transparency of the required size already, we make the final negative by contact. The advantage of the first method is that with direct contact by copying the original negative we save on material, the advantage of the second method is that we can easily touch up the enlarged transparency.

We will develop in a normal positive developer, choosing a developing time for the transparency so that we acquire a transparency of approximately normal gradation. In the second stage, when developing the final negative, we choose a developing time in order to achieve a sharpness suitable for our technique used. The two-stage process of preparation of a duplicate negative has the advantage that we can once and for all prepare transparencies from original negatives and then we can prepare negatives of various contrasts from them, according to which copying technique we want to use.

Normal frame cut film, such as Kodak T-Max 100, is sometimes used as a material for creating transparencies and the final negative. A disadvantage is that the materials are panchromatically sensitised and it is necessary to work with them in darkness. If we don’t have any excess stocks of such materials, it’s better to get some orthochromatic film which we can work with under red light.

Since successful and problem-free preparation of the negative is almost key for historical photographic techniques, at NTM we tested whether it is not possible to use some lesser known materials, used for scientific, technical or medical purposes, supplied by the domestic manufacturer Foma Bohemia for these purposes. Here such material could be more financially accessible than, for example, the foreign Ilford Ortho Plus. In the end, we found that Foma supplies orthochromatic films for medical purposes which, in terms of characteristics, suit hand processing in a basin with normal positive developer.

The material is Medix PT, an orthochromatically sensitised cut film intended for monitor photography. Foma supplies it in 8 x 10 inch format (approximately 20 x 25 cm). It is supplied in packs of a hundred, the current price is about CZK 2 300, that is, at a price almost the same as we would pay for the same size cut film Fomapan 100. In the case of great demand it would probably be possible to agree with company representatives on distribution in smaller packets. According to the response of the sales division of the company this material will still be on the market for at least two or three years. No one knows what will follow, classical photography is now used less in the medical environment.

The film is very easy to work with; it has a thickness of 0.15 mm on a solid base. It is developed in a basin; at NTM we developed it using Fomatol P positive developer diluted 1:1. To achieve a normal contrast transparency (from a normal contrast 35mm negative) the developing time is around three minutes. Since the material is intended for photography it is very sensitive, the sensitivity is probably around 50 to 200 ISO, according to the heaviness of developing. This sensitivity also corresponds to microsensitometric characteristics, thus grain as well, which is greater than with less sensitive films. For that reason it is better to prepare a transparency of the negative at the definitive size, thus not by contact from 35 mm, where grain size could be disruptive.

A technical sheet is available at the manufacturer’s website (www.foma.cz).

Alternative process with heavy lithographic film

With certain knowledge of photographic materials and their processing we can use normal lithographic film to create a duplicate negative. Work with it is of course very difficult, since it is not intended for the purposes of halftone reproduction and has high contrast. If we venture to use it as a halftone material, we must process it in a special developer with a modified method. It is not enough to use normal diluted developer, since smudges will appear in the picture and the process is unstable – even the density check and the negative developed based on it are different.

Since at NTM we have acquired a large amount of old Agfa lithographic film from a former printing shop, we have elaborated that the procedure in detail. It was necessary to find a developer which works slowly and uniformly (without smudges) in a suitable concentration. Only non-alkaline metol can be considered – metol develops in an acidic environment as well. For greater stability hydroquinone is added to the developer. The developer is prepared from two durable stock solutions:

We prepare the working solution by mixing 2 parts MZ with 1 part HZ and 10 parts water. The developing time is selected according to the contrast we want. For reasons of uniformity of density it should be at least five minutes. If the result is too soft, we dilute the stock solutions less (in place of 10 parts water we add, for example, only 5). We can dilute the developer for a longer period in advance. For stability of results we should use it only once – for development of each film sheet we use only a little developer which we then pour away.

Using the given procedure we achieve a completely uniform picture without any smudges.

Despite a lot of difficulty, the use of lithographic film for making transparencies and duplicate negatives is very popular among students abroad. It can be purchased for a fraction of the cost of normal frame material.

Procedure with a normal positive on RC paper instead of a transparency

The two-stage process of preparation of a duplicate negative can be made simpler, if we have a suitable positive on current regular RC photographic paper.

We copy it with the light of an enlarger by contact under glass on a suitable film material (for example on the mentioned Ilford Ortho Plus or in the mentioned process with lithographic film). Of course, we achieve a picture laterally inverted. In view of the fact that the sensitive layer of film on which we are copying is in direct contact with the layer of the copied positive, the sharpness is good. We must weigh down the glass well. Even photographs on RC material have a tendency to curl and stick out in some places, which reduces the sharpness.

Positives on RC paper are more suitable for this purpose than on classic baryta paper. The latter has any more distinct structure; it is thicker and thus requires longer exposure. That’s why making it translucent just using oil is sometimes recommended. However, this method has the disadvantage that, again, the oil makes the structure of the paper distinct.

For classical calotype paper negatives warmed wax is used for purposes of translucency. By using wax we can achieve a significant clarifying of the paper, as with oil, but we have to accept the fact that the picture will have irregularities given by the basic structure of the paper.