Obsah

Part I - Historical photographic processes

Part II - Basic processes 1

  • Paper sensitising
  • Application of the sensitising solution with a brush
  • Choice of a good brush
  • Foam plastic brush
  • Glass rod
  • Sensitising by soaking the paper on the surface of the solution
  • Selection of paper for sensitisation

Part III - Basic processes 2

  • Options for negative preparation
  • An original negative made by a direct photographic camera
  • Enlarged duplicate negative
  • Procedure with cut film
  • Alternative process with heavy lithographic film
  • Procedure with a normal positive on RC paper instead of a transparency

Part IV - Basic processes 3

  • Negatives prepared with digital technology
  • Exposure
  • Copying frame
  • Source of light for exposure
  • Checking exposure
  • Processing
  • Affecting the contrast of a picture with chemicals
  • Reducing an image created with silver
  • Washing-out and possibilities of its acceleration

Part V - Salted paper process

  • Principle
  • Colour of the picture
  • Permanence
  • Requirements
  • Preparation of the negative
  • Selection of suitable paper
  • Paper sensitising
  • Exposure
  • Developing
  • Fixing
  • Washing out and possibilities of its acceleration
  • Drying
  • Toning
  • Conclusion

Part VI - The Van Dyke Process

  • Sensitising solution
  • Paper
  • Paper sensitising
  • Exposure
  • Development in water
  • Fixing
  • Washing out
  • Drying
  • Toning

Part VII - Cyanotype

  • Principle
  • Durability and archiving
  • Working procedure
  • Working sensitising solution
  • Paper for sensitising
  • Paper sensitising
  • Exposure
  • Processing
  • Drying
  • Reducing an overexposed picture
  • Toning

Part VIII - Historical photographic techniques at the National Technical Museum, Prague

  • Calotype
  • Salt paper photograph
  • Wet collodion process
  • Ambrotype
  • Ferrotype

Part IX - Historical photographic techniques at the National Technical Museum, Prague

  • Albumin paper photography
  • Platinotype
  • Pigment printing and carbon printing
  • Bromoil printing and bromoil transfer printing
  • Creative workshops in historical photographic techniques at the National Technical Museum

HISTORICAL PHOTOGRAPHIC TECHNIQUES IV

Basic processes III

Negatives prepared with digital technology

Digital technology has nothing to do with historical processes. Many of us who want to enjoy making photographs on handmade paper will probably not be too bothered by that fact. The final picture is printed on paper prepared by a technique used in the 19th century.

Less and less people today have a darkroom at home or use a wet process. Preparation of a classical silver halide negative is difficult or even impossible for them. It would be a pity not to use the simple possibilities of older processes just because our work is not purely historical.

If we are able to make negatives without a darkroom, the field of historical photographic techniques opens up for a wider circle of people. Therefore, even people who have never tried classical photography, but have an interest in creative techniques and picture making and can themselves try some of the processes. Today there are many people taking photos digitally. Any digital picture can be used for creation of a negative required for our purposes. By means of programs for modifying photographs we can arbitrarily influence the contrast of a picture and reproduction of tones and significantly modify the characteristic ‘curve’ of the picture.

For initial tests we can print negatives on a transparent base on a home ink or laser printer, it is better to give more complicated work to a professional digital minilab, although here minilab workers are unlikely to have much experience with these kinds of orders. We recommend finding out more information at www.alternativephotography.com and www.unblinkingeye.com on the processes used abroad. These days, digital negatives are considered widely in literature. We ourselves at NTM have not finished the technique of creation of digital negatives so far, so we cannot refer to our own experiences.

Exposure

With direct copying processes such as cyanotype, salt process, albumin process and Van Dyke, the picture appears directly in the course of copying. That’s why these processes were known as “visible copying” in period literature. We can therefore visually check the course of picture creation. That possibility is a great advantage and clearly was one of the reasons why direct copying contact processes (chiefly collodion papers) were used for a long time, even in times when highly sensitive development gelatine papers, which are used until now, were already widely available. If we copy in daylight, then in view of the fact that UV radiation is partially absorbed by light, we cannot expose inside a window. We should expose outside with the sky above, for example on a balcony.

Copying frame

We copy on sensitised paper by a contact method. During this the sensitive layer of the negative is in close contact with the sensitise surface of the paper. The contact of both layers should be as tight as possible. In places where the contact of the negative with the sensitised paper is not full, there will be no sharp delineation. If we have just started these processes, for our first attempts it is enough to weigh down the negative with normal glass of a maximum thickness of 2 mm. If we require pictures to be perfectly sharp across the whole surface, we will need a copying frame intended specially for this purpose.

It is composed of a wooden frame with inserted glass and a wooden base with felt which, by means of springs, presses the negative to the glass. The frames usually have a wooden base which is separate and hinged, so that it is possible to check the increasing coverage of the picture during exposure (see figure).

Frames for copying photographic negatives used to be manufactured in great quantities and various formats. We can sometimes find frames of smaller dimensions in photography bazaars, though larger ones are more difficult to find. For a more skilled handyman it shouldn’t be too much of a problem to make a similar frame from an ordinary picture with a wooden frame. Nowadays frames are specially manufactured for these purposes abroad. If there was a demand for them here, we would surely find a manufacturer for them in time.

Source of light for exposure

We know that direct (visible) copying processes are much less sensitive than modern photographic papers. That is why we must copy the negative onto them with intensive light by contact. They are most sensitive to ultraviolet radiation in the A spectrum – wavelengths of 320 – 400 nm. We thus need a source of light whose spectrum includes at least part of the UV A spectrum.

Daylight contains a sufficient share of UV A. Formerly photographers had no other source of light for copying, so they copied exclusively in daylight. Photographic studios had large copy rooms where copying frames with negatives of various sizes stood in rows.

Exposure in direct sunlight can take from several minutes to an hour, according to the density of the negative and type of process. During cloudy weather in winter it usually takes an hour, for denser negatives it can take several hours.

The colour temperature of the light affects the contrast of the resulting picture. Pictures copied under a cloudy sky or clear sky, but in the shade, have more contrast than pictures copied in direct sunlight.

If we are going to try historical processes occasionally just for fun, daylight will probably suffice. If we want to copy more often and regularly and we don’t want to depend on daylight, we can purchase our own source of UV light. Abroad there are several types available on the market for these purposes. We can also use a home sunray lamp or create our own source of UV light. You can find detailed guides for this on the internet (see www.unblinkingeye.com).

At NTM we used 60 cm Black Light Philips Actinic fluorescent tubes (used at discos). We installed four fluorescent tubes in the sheet metal casing of a normal fluorescent lighting unit about 3 cm from one other (see figure). The equipment is sufficient for uniform illumination to a format of about A4. Exposure is between 5 and 20 minutes according to the copying technique and density of the negative used. For larger formats more tubes would be necessary. Aside from fluorescent tubes there are other options – see unblinkingeye.com. We should hire a qualified electrician for the electrical connection when installing the tubes.

Intensively UV radiation damages the eyes. Warning: never look directly at a source of UV light with unprotected eyes! For even regular work with a UV source we should wear sunglasses which reliably filter out UV radiation (bought at an optician’s). Healthy eyes are an essential tool for the photographer.

Checking exposure

In order to check the density to which the picture has been copied, we disengage one of the springs from the back of the copying frame and pull out one of the parts of the wooden base. We remove the negative and paper on which it is copied and assess the picture (see figure). Though the picture will not look completely the same as when finally prepared and dried (density and colour will change a little), with experience we will soon learn how it differs and the density which we need to achieve during exposure.

Processing

The fact that historical processes are sensitive only to UV radiation allows us to work with them under very weak tungsten light, which makes the whole process easier.

If we work with a direct copying technique, such as salt, albumin or Van Dyke, we develop (or rather wash out) in ordinary water. After that we fix in a weak solution of thiosulphate, then rinse and dry.

Developing processes such as kallitype or platinotype require processing in special baths.

High-grade prints are processed by rinsing the picture with water and transferring it onto other papers (pigment print) or by applying colour to the washed relief of the picture and then transferring to the intended base (oil print, bromoil print).

Affecting the contrast of a picture with chemicals

The contrast of a picture can be increased to a certain extent by adding an oxidation reagent to the sensitising solution applied to the paper or with some techniques to the developing bath. Traditionally potassium or ammonium dichromate was used for this purpose.

We should point out that dichromates are considered as highly toxic and carcinogenic today. If, despite this, you decide to use them, you should work in a fume chamber or at least with a mouth-screen as protection against inhalation of dust particles of the material. Since they are toxic, dichromates are not used today and are replaced by other materials with the same effects, for example, potassium chlorate, today exclusively used for regulation of contrast in the platino-palladiotype process. In some cases hydrogen peroxide is used, either as an addition to the sensitising solution or developing bath.

Preparation of a set of solutions of the given materials of various concentrations is recommended (usually 0.125 to 3%), so that it is possible to affect contrast by adding several drops of the given solution to the sensitising solution.

A disadvantage of increasing contrast with chemicals is that the increase of gamma does not occur uniformly for light, middle and dark tones. It seems that it functions only so the light grey tones emerge as white, giving the impression of increased contrast. Contrast in the darker and darkest areas of the picture remains almost unchanged. Actual increase of contrast does not actually occur and the transfer of the tone scale is deformed. Exposure should be extended (at least twice).

A further disadvantage of increasing contrast by adding an oxidation reagent to the sensitising or development solution is that you often get a grainy image.

At NTM we tried to increase contrast by means of potassium dichromate with the salt process. The results seemed to confirm the stated facts, but they were not too convincing or reliable.

We recommend making great efforts in the preparation of a negative with corresponding contrast, so that we are not forced to increase it later in the process. In terms of their basic techniques historical processes are quite delicate and require time-consuming testing. If we add testing of methods of increasing contrast by chemical means, combinations of procedures will become complicated and in the end we will have spent more time on testing than actually creating any nice pictures.

If we work with several types of copying techniques, we will have positive transparencies from previous preparations of negatives and from them we can with a little effort prepare a new duplicate negative by contact, with the contrast required for the next technique which we want to try.

If we prepare negatives for digital copying, the final selection of contrast is very easy and we can carry it out in a few seconds.

Reducing an image created with silver

As in the case of modern gelatine positives it is possible to reduce pictures made with historical copying processes with an image created from silver.

Reducing is a very advantageous and useful process. Often during exposure of a picture we’re not able to precisely estimate the density to which we should copy and only after processing and drying of picture we find that our estimate is incorrect. If the picture is denser than is required there is a quite simple correction available by reducing. If we are careful and don’t hurry, we can do it without risk of damaging the picture and without any reduction of its durability.

If we master the technique of reduction, which is quite simple, if we are not sure how much to expose, we can expose a little in excess and, if necessary, reduce the picture later.

The principle is actually the same as the classic Farmer's Reducer. Potassium ferricyanide blanches the required amount of silver forming the picture and the arising compound is dissolved with sodium thiosulphate. Farmer's Reducer is usually prepared by mixing a reserve concentrated solution of potassium ferricyanide and reserve concentrated solution of thiosulphate, and subsequent diluting to a concentration with which the process occurs with suitable speed.

At NTM we found that for pictures made with historical techniques it was better to modify the classical method of reducing and work in two phases. First we blanch the picture in a very weak solution of potassium ferricyanide and then we fix in a solution of thiosulphate. We then have greater certainty that we are not reducing too much and that the fixing will be adequate – this need not be the case when using very dilute reducer in one solution.

Stable stock solutions:

I.
Potassium ferricyanide 10g
Water up to 100ml

The solution can be stored in a plastic dropper bottle.

II.
Crystal sodium thiosulphate 500g
Water up to 1000ml

When reducing we proceed as follows: We add 100 ml to a photographic tray and 10 drops of potassium ferricyanide solution. We put the photo into it (dry or wet) and watch it reduce. We should finish the process sooner rather than later – the density of the picture can be judged best when the copy is dry. If necessary, we can reduce again. With denser pictures the weak solution of potassium ferricyanide will be exhausted and the reduction will stop. In that case we should prepare a fresh lot, repeating as necessary. If we judge that the density of the picture is already sufficient, we can rinse the copies and fix them in a 2.5% solution of thiosulphate for about 3 minutes. We prepare it by diluting a 2nd stock solution in a ratio of 1:20 (after use we should pour it away). We wash it for 10 to 20 minutes (according to the paper thickness) and dry in the usual way.

By reducing several exposed copies we acquire copies indistinguishable from copies exposed normally and processed in the normal way. Possibly they will brighter, with purer light. It is definitely worth embracing the process of reducing. Potassium ferricyanide is a common chemical material (though classified as damaging to health, it is not considered as poison), we can use sodium thiosulphate from the packet of a classical acidic fixer (the crystals in the larger bag are sodium thiosulphate; the ones in the smaller are potassium pyrosulphite).

Washing-out and possibilities of its acceleration

After fixing with thiosulphate for accelerating washing-out we recommend including a bath for accelerated washing-out. Commercially available baths are available abroad, for example Kodak Hypo Clearing Agent. After removal from the fixer the copies are washed for about 5 minutes, and then they are immersed in the commercial bath (essentially a solution of sodium sulphite). If we don’t have a commercial bath, we can use a 1% solution of sodium sulphite (pour away after use). It is stated that washing-out can be reduced to a half of the normal recommended time.

We can best wash a copy on paper in an ordinary tray. We cannot recommend washers common to normal photography where the pictures circulate in flowing water, since pictures on fragile paper can tear with sharper movement and abrasion against one another or the walls of the washer. Washing in running water has no essential advantages. It uses a lot of water. Furthermore, air bubbles remain stuck on the surface of the picture, under which washing fails to occur.

Therefore it is better to wash in a simple tray, move the picture about often and wipe any bubbles from the surface. Every few minutes we should change the water, according to the technique and paper thickness. Though it is better to work with thicker paper during the whole process, it needs to be washed for longer, since chemical residues are soaked into it more deeply.


Text and photografy Ing. MgA. Tomáš Štanzel. Translated by Nicholas Miller © PhotoArt.
The author works as a curator of the Department of the History of Photographic
and Film Technology at the National Technical Museum in Prague and in the scope of his work
he is also involved in the program "Reconstruction of Historical Photograph Techniques".

Contact:
National Technical Museum
Kostelni 42
170 78 Prague 7
Czech Republic
tel.: +420 220 399 179
tomas.stanzel@ntm.cz

 

National Technical Museum