Mastering Gum Print – Book 1: Monochrome Printing – Historical & Alternative Photography
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Preface

Gum print, gum dichromate, or, using the old name of “gum bichromate,” is another of the old photographic processes and is quite popular among the enthusiasts of photography.

With this technique, we can print both black and white as well as color photographs, and, most importantly, with this photographic technique we can achieve one of the greatest tonal ranges on photographic prints.

We should mention, of course, that photographers in the period of Pictorialism also admired gum printing for a completely different reason. Gum printing enables unprecedented freedom in the manual processing of images, which of course brings photography as close to the art of painting as possible. In the words of one of the greatest masters of gum printing, Robert Demachy (1859 – 1936), “For it must be well understood that a gum print, if not interfered with during development or the first stage of drying, is not worth the trouble taken to make it.”

Unfortunately, the technique of gum printing is a bit complicated because there are dozens of factors that affect the final look of the photo. The process of gum printing, therefore, cannot be described with a few simple, generally applicable recipes or formulas, but it can be presented only with complete guidelines, in the same way that the master directs the apprentice along the path to mastery.

And such an approach is chosen for delivery in this book. The reader will need to carry out a series of well-described procedures through which he will be introduced to the technique. He will learn about various factors that can lead to failure, and, of course, at the end he will have a database with which he will be able to create a master photo without difficulty.

In this, the first book on gum printing, we start by describing how to determine the optimal recipe for printing gum prints, how to solve a variety of problems that lead to failures, the production of single layer photos, and finally the printing of multi-layered images that allows us to make photos with a maximum possible tonal range.

Those chapters are followed by chapters with descriptions of the manual processing of photos and descriptions of advanced techniques, in which various color hues are used.

The book is, in short, a kind of “master class” of gum printing, and not just because of the precise and progressive description of the various techniques, but also because of the descriptions of pictorialist procedures that are almost lost today. If you were, for example, to search for documentation on the whiteness on a photo or manual processing of photos, etc…, during the pictorialist period as a basis for making gum print, we are disappointed today to find that these procedures are not described any more in any of the modern texts.

In the modern literature on gum printing, we also observe significantly different recommendations and information that is quite different from actual results. In this book, therefore, these differences are thoroughly described and presented with simple tests that can be performed by any interested reader.

With the hope that gum printing will become somewhat less “complicated”,

Peter Mrhar

A brief history of gum printing

The development of the gum bichromate or gum dichromate process, or gum printing, began in 1839, when the Scottish scientist Mungo Ponton (1801-1880) discovered that a photo can be produced using sodium dichromate. Soon after, William Henry Fox Talbot (1800 – 1877) discovered that the gelatin and gum arabic in contact with dichromate hardens, but a first real modern gum print was made by French chemist Louis Alphonse Poitevin (1819 – 1882), who, in 1855, added a pigment to gum print emulsion. But the development of gum printing did not stop with black and white photography. John Pouncy (1818 -1894) used colored pigments for the first time in 1858 and created the first color photograph.

Because of the quite blurry images produced by gum printing compared with the daguerreotype process and albumen prints, gum printing soon sank into oblivion. Its true success was reached only at the end of the 19th century. With changes in artistic views and with the onset of Impressionism, this blurred feature of gum printing became highly desirable.

After 1895, when Robert Demachy exhibited his first “painting” photos, gum printing became one of the most popular photographic processes. The quite popular impressionist properties of gum prints were, of course, also used by other masters of Pictorialism, such as Constant Puyo, Theodor and Oskar Hofmeister, Rudolph Duhrkoop, Hugo Erfurth, Aleksei Mazurin, Sergei Lobovikov etc… But only the Austro-Hungarian photographers Heinrich Kuhn (1866 – 1944) and Hans Josef Watzek (1848 – 1903) brought gum printing to perfection. They were the first who made multi-layer photos, a technique which tremendously increased the dynamic range of gum prints.

Development of gum printing techniques continued for a few years. In the year 1894, Victor Artigues put a paper with a slightly more concentrated emulsion with less colloid up for sale. Because of this and because of the development in water to which was added wood dust, the photo became grainy, with a matte surface, and with a rather high dynamic range. This technique, so-called “carbon print without transfer,” which is most commonly known today as the Artigues-Fresson process, was further refined by Théodore-Henri Fresson.

The popularity of gum prints began to decline around 1904, when oil printing became an increasingly popular procedure, along with the somewhat less-demanding technique of bromoil, which results in a process in which oil paints are applied to the colorless gum dichromate emulsion. The final decline of gum printing was caused by the rise of the Modernism movement and the Avant-garde movement. With the discovery of the new visual language of photography, Pictorialism became, with its desire to mimic impressionist painting, only the subject of insults. This was a period of bold ideas within the Avant-garde movements, and so the old historic photographic processes made room for new artistic ideas and concepts.

A few words about the process

Gum printing is a process in which we spread a mixture of three components onto paper: colloid (gum arabic, gelatin, albumen, or glue, etc…), a pigment or color, and potassium dichromate, which changes the solution into a light-sensitive emulsion, and is the most commonly used third component at the present time.

When the paper is exposed to UV light in a contact frame, the illuminated colloid (usually gum arabic), under the influence of potassium dichromate, solidifies while unexposed portions remain soft, so that they can be washed away in water. Only an image made of hardened, pigmented colloid remains on the paper.

But, because such a single-layered photographic process has a very small tonal range, with very short gradation, we need to add some additional layers of different tonalities to the photograph. In most cases, we will discover that a black-and-white photograph consists of at least three layers: a layer of midtones, another of bright tones, and a third layer with dark tones.

In books which describe the procedure of gum printing, we will often notice the fact that every photographer uses his own technique and his own recipes, and that there is no recipe that would work for all people in the same way. This is, indeed, true. Gum prints are affected by so many different factors that we will never succeed in producing two identical photos. Because of this, we will describe in this book only the most commonly used materials and the most popular recipes, but in such a way that the reader will be able to make a gum print masterpiece by the end of the book.

What do we need?

Basically, to produce photos with this procedure, we will need only a few devices and little material.

Colloid

The most commonly used colloid is the best-quality gum arabic, which should be of the Senegalese type. We can prepare the gum solution ourselves, but most commonly it is obtained as a ready-made, undissolved gum arabic of better quality for artists (see Gum arabic).

Pigment

We may read about dozens of different descriptions and recommendations concerning colors, but almost all the authors recommend the use of watercolor paints in tubes, because the mixing of these colors with gum arabic is much easier than the dissolution of pigments in the solid state (see Colors in gum print).

Potassium dichromate

To sensitize the paper, photographers in the last century as a rule used two chemicals: ammonium or potassium dichromate. However, since almost 100% of photographers nowadays use only potassium dichromate, we will focus on this option, as well (see Potassium dichromate).

Tools

To create gum prints, we do not need a lot of tools and accessories. To begin with, we will need a tray for washing (developing), which must of course be larger than the paper, a few brushes, a negative, a contact frame, preferably a UV exposure unit, a pot for heating gelatin, and some glasses.

Gum Print

Warning. Prior to each production and use of chemical solutions, it is best to read the instructions and warnings. Information on safety, the so-called MSDS (Material Safety Data Sheet), can be found online or in relevant manuals.

Paper

For making gum prints, we can use almost any paper, but we most often use artistic paper for watercolor paintings, which is made of 100 % cotton. This paper will remain unchanged even after a few centuries, and what is most important, it does not fall apart even after a long-term treatment in water. Another advantage of artistic paper is, of course, its beauty, which gives an additional charm to the photo.

The texture of the paper

Paper is manufactured in various ways, and most commonly the texture is a result of using different methods of rolling paper pulp. Some papers are quite smooth (hot pressed – 1), others less (soft pressed – 2), still others have a slightly noticeable relief (cold pressed – 3), and the fourth type of paper has an extremely rough texture (rough – 4).

Gum Print

To create a gum print, in the opinion of photographers of the last century, the most appropriate papers were of medium-coarse texture (2 and 3). In the papers with rough texture, bright spots on the tips of the texture are quite quickly observed, and the pigment is washed away. On plain papers, however, the beginner will often experience difficulty in applying the emulsion. Of course, these are only recommendations. With a variety of paper textures, we can create various types of images. Photos on smooth, hot-pressed paper are much sharper (5) than photos printed on rough, cold-pressed paper. The latter photos are much more blurred, and we can even say softened (6).

Gum Print

Paper thickness

We can buy paper in various thicknesses. The easiest is to work with an extremely thick paper, because it does not wrinkle and it remains flat even after prolonged treatment in water.

Right and wrong side of paper

Most of the art papers have a “right” and “wrong” side. On more expensive papers, the “right” side is recognized by a watermark showing the name of the manufacturer. If the text of the watermark is turned correctly so the name can be read, then the “right” side of the paper is facing us. On cheaper papers, the “right” side is usually smoother and its surface is better for treatment.

Paper size

Due to the rather blurry image of gum prints, there is a rule saying that the gum print photo must be printed on quite a large sheet of paper. Following the recommendations of the masters of the last century, the print should be at least 20 x 30 cm in size.

When deciding on the format of the paper, we have to choose a paper that is larger than the size of the photo. Most often, we have to leave at least 5 centimeters of empty space at the edges because we need enough space for the application of the emulsion. In the case of a multi-layer print, we also need the edges to print the registration marks or to make pin-holes for registration purposes.

Paper problems

In relation to the paper, we may encounter a few problems. The photographers of the last century already observed that freshly-made paper is much less problematic than older paper. The properties of the coatings on the paper, in fact, change over time, so that a print on the same but aged paper can be different from a print on a newly-manufactured paper. Of course, the change in the print quality is even greater if the paper is improperly stored, for example, in excessive moisture or at excessive temperatures, or if it is exposed to light.

Shrinking the paper

As a good paper is made of cotton, like fabric, it will shrink in the first extended immersion in water and subsequent drying. This, of course, plays no role in single-layer printing, but it is recommended that we shrink the paper in any case.

Shrinking the paper is, of course, obligatory for printing multi-layer gum print as it prevents the further expansion of the paper that occurs during the processing of multiple layers in the water. Differing paper sizes make it impossible to accurately register the negative on the previously printed image.

Prior shrinking of the paper is also recommended for the verification of certain data concerning the quality of the paper.

  • If the paper sinks to the bottom of the tray, it is probably not made of 100% cotton. In any case, we cannot develop a photo that is attached to the bottom of the tray.
  • Another important piece of information is the flatness of the paper. If the paper is too curled when it is dry, we will have problems applying the emulsion and placing the negative on the paper, etc… If the paper is too wrinkled, it’s best not to use it.

The technique of shrinking

Now that we have established the basic properties of the paper, we will describe a simple technique for carrying out and then checking the shrinking of the paper. If we rely on the information of others, we will very often be disappointed.

The paper is shrunk by immersion for 1 hour in water heated to 50°C and subsequently dried with hot air. If the paper shrinks a great deal in the first soaking, we must soak it again in the same conditions. And most often, the double soaking is almost mandatory.

Checking the shrinkage

The papers of various manufacturers change size differently. Some papers are unlikely to shrink, while with others we have to repeat the shrinking 3 times if we want the size to be unchanged in consequent manipulations in water.

The method for measuring the shrinkage is, of course, very simple.

  1. On the back side of the paper, we place a ruler along the vertical and horizontal edges of the paper and draw tick marks with a pencil (1). In our case, we have outlined marks along a distance of 50 cm in the horizontal direction (A to B) and along the vertical direction at 45 centimeters (C to D).
  2. We pour water heated to 50 °C into a tray that is somewhat larger than the paper size. We put the paper into the water, where it is left for 60 minutes (2). When we place a larger number of sheets into the bath, we move the bottom paper to the top after a few minutes, so that all sheets are evenly soaked in water.
  3. After one hour, we take the paper out of the water.
  4. The paper is then dried, first in air and finally with hot air from a hair dryer.
  5. When the paper is dry, we place a ruler on the paper and measure the distance between the previously marked lines (1).
  6. We write the data on the extent to which the paper has shrunk (3) in a blank table (4). For example, we find that in the first soaking, the Bergger COT 320 paper shrunk on the long side by 1.5 mm and on the shorter side by 0.5 mm. The Fabriano Artistico paper shrank even more, by 6 and 3 mm.

Gum Print

Gum Print

  1. The method of shrinking for testing purposes is repeated yet one more time.
  2. When the paper is dried after the second soaking, we re-measure the distance between the previously sketched marks. We immediately see that the second shrinkage is much lower, but still present. After the first shrinking of the Arches Aquarelle Grana Fina paper, for example, the long sides shrank by 4 mm, while after the second soaking it shrank by an additional 1 mm. After two rounds, therefore, it shrank by 5 mm.

Surface sizing of paper

Although there are quite a lot of art papers with surfaces coated with one of a variety of protective layers, this layer quite often does not prevent the penetration of pigment or color into the paper. In this case, the color is so fully absorbed into the paper that it is virtually impossible to remove it from the image. In this way, we will observe a loss of all the bright tones on the photo (1).

Properly selected and applied surface sizing on the paper is, therefore, a first condition for achieving a high-quality photo. This protective layer must, in fact, allow almost complete washout of the color from the paper (2), whereby some pigment must still be retained so that the picture remains visible. If the surface of the paper is too smooth, the image will be partly (3) or fully washed away from the paper. This, of course, we do not want to happen.

Gum Print

The number of layers of sizing we apply to the paper, of course, depends on several factors. But most often, we apply two layers of diluted gelatin, as described below. In this way, we avoid possible lines that remain after brushing, and the second layer may also cover a part of a previously poorly-coated surface (4). Another advantage of two layers lies in the fact that the characteristics of the paper, under such strong protection, almost do not change whatsoever. That means that we can most probably use the same photo-emulsion recipe without substantial changes. In this way, of course, we avoid re-testing the emulsion.

Gum Print

We apply this protective layer coating on any paper that we have shrunk with the procedure detailed in the previous section. When we shrink the paper, the gelatin or starch (which is frequently used for sizing), is often washed away.

Creating the sizing

Making gelatin sizing

During the last century, the most commonly used protective layer was made of 3 to 8% gelatin with the addition of alum or formalin (which is a 37% solution of formaldehyde (HCHO) diluted in water). The formalin or alum is used to harden the gelatin, so that in the processing of the photograph, the coating does not wash away from the paper. One of the recipes which was also used by the Pictorialists, and is sufficient to coat approximately one layer on four sheets of paper of size 50 x 70 cm, consists of:

  • 150 ml 3% gelatin
  • 1.5 ml formalin (or 3 ml of 5 % alum solution)

Making a gelatin solution

The gelatin used in this solution is a simple kitchen gelatin. We will need a 3% solution of gelatin, which is made according to the manufacturer’s instructions or according to the procedure described below. For making a gelatin solution we need the following:

  • 30 g gelatin
  • 1000 ml water
  1. From the specified 1 liter of distilled water, we pour approximately 100 ml into a small bowl. Then we slowly add 30 g of gelatin (1).
  2. We wait 15 minutes for the gelatin to thicken.
  3. Then we place the bowl of gelatin into a pot of water heated to about 45°C (2).
  4. When the gelatin liquefies, we stir it slowly for a few minutes.
  5. We carefully pour the gelatin solution into a bottle.
  6. When reheating the gelatin solution in the bottle, the label with information will probably peel off the bottle, so we write the basic information about the solution on the stopper (3).
  7. We tightly close the bottle and put it in the refrigerator. Gelatin stored this way can be used for several weeks.

Gum Print

Making a gelatin sizing solution

Creating a sizing solution according to the recipe above is, of course, very simple.

  1. If the gelatin is solidified, it is first liquefied by placing the bottle containing the gelatin in a water bath at 40°C for 15 minutes (4).
  2. When the gelatin is heated and becomes liquid, we pour 150 ml of gelatin into a glass (5).
  3. Then we add 1.5 ml of formalin (6) or 3 ml of 5% alum.
  4. Once the solution has been slowly stirred and becomes well-mixed, it is ready for application.

Gum Print

Other chemicals used for hardening gelatin

As we previously mentioned, at the end of the nineteenth century, photographers also hardened gelatin with a chemical compound which bears the name of alum. Most commonly mentioned compounds are chrome alum (KCr(SO4)2•12H2O) and potassium alum, or more correctly called aluminum potassium sulfate (KAl(SO4)2•12H2O).

These compounds have two major advantages over other hardeners: they are non-toxic and inexpensive. We should also mention the bad side of chrome alum: it leaves a slightly bluish tint on paper.

When we want to use alums, we first make a 5% alum solution, as follows: dissolve 5 grams of alum in 100 milliliters of water. The solution is stored in a bottle and then, if necessary, used in place of formalin.

The next hardening compound is glyoxal (OCHCHO), which is the modern substitute for formaldehyde and is mentioned in the book Alternative Photographic Processes. This compound has two disadvantages: it is about as toxic as formaldehyde, and furthermore, it is quite unstable, as is mentioned in the same book.

Warning. Formalin is toxic if ingested or inhaled and will cause severe skin burns and eye damage if it comes in contact with skin or eyes. Prior to using the chemical, read the appropriate instructions and warnings. Wear appropriate protective equipment.

Arrowroot sizing

Another solution that is used to protect the surface of paper is arrowroot solution, which is also mentioned by Robert Demachy, one of the greatest masters of Pictorialism. We will need the following:

  • 3 g arrowroot
  • 100 ml water

The production of this solution is similar to the manufacturing of a gelatin solution:

  1. We mix 3 grams of arrowroot with an approximately equal quantity of hot water. In this case, for example, we mix the mentioned amount of arrowroot with one tablespoon of water so as to obtain a thick paste.
  2. We bring the remaining water to a boil, and while stirring constantly, we slowly add the previously made mixture.
  3. The mixture is heated for about 5 minutes, while constantly stirring at a slightly lower temperature than the temperature of boiling.
  4. After that time, the arrowroot solution is left to settle and cool.
  5. Before using the arrowroot solution, we need to drain it.

Following the recommendation of the masters of Pictorialism, it is best to make just as much arrowroot solution as needed. The remaining solution is discarded.

We most frequently apply arrowroot solution in two or three layers, as described below for the application of gelatin. The only difference is that we need to apply the arrowroot smoothly, using a soft brush and working quite persistently, as we have to completely dissolve all the pieces of arrowroot. Otherwise, tiny black dots will appear in the photograph.

Application of sizing

When applying a protective layer, we need to be very careful, as an unevenly coated layer largely affects the image quality. Special care should be taken in the duration of application, since the protective layer will dry very quickly in most cases.

In the case of protective coating or sizing which is made from gelatin or arrowroot, we apply the coating with two brushes. With the first brush, we spread the solution over the paper and with the second, a very soft brush, we smooth the surface and remove any bubbles and lines left by the first, hard brush.

The sizing is applied and dried in a very clean place, because we don’t want any particles of dirt to fall onto the paper.

A method for applying the sizing is as follows:

  1. First, we thoroughly clean and vacuum the space in which we are working. When working in the open, the atmosphere must be calm.
  2. We place the paper on a large flat surface over layers of newsprint, so that there are a few centimeters of empty space around the paper (1).

Gum Print

  1. Before we begin to apply a sizing, we draw a small “x” on the back side of the paper, so that we will know which side of the paper was coated and which was not.
  2. Then we pour a small amount of solution onto the sheet of paper and with quick strokes with a larger, stiffer, flat brush, we apply the solution to the surface. Then with up-and-down and left-to-right movements, the layer is applied evenly over the entire surface of the paper. At each stroke of the brush, we continue all the way over the edges of the paper, so that the layer is evenly distributed, including at the edges (2).

Gum Print

  1. Then we take a brush with very soft hair and smooth the surface to remove all the air bubbles from the paper. This time, the movements of the brush are slightly different, as if we want to sweep away dust. Now, with the brush barely touching the surface, the movement takes place only in one direction (3).
  2. Once we have coated the paper, we dry it in a dust-free space.

Gum Print

Warning. Since formalin is quite toxic and volatile, we apply gelatin sizing in well-ventilated areas or outdoors. Do not forget about the appropriate personal protection.

Colors in gum print

The most important basic property of colors used in gum printing is that they are soluble in water. Another important property is staining, or the ability to wash the pigment away from the paper, the third is lightfastness, i.e. resistance to light in time, and the fourth is the quality of color.

Types of colors

The masters of gum printing most frequently added watercolor paints to their light-sensitive emulsions. And so it is today. We have observed that professional watercolor paints in tubes are the most commonly used, as they are, in most cases, of better quality than the ones we make by ourselves. But if we have pigment powder and a magnetic stirrer at our disposal, we can make gum print colors without a problem.

Another quite popular type of color is so-called tempera paint. This is nothing more than a kind of “watercolor” paint in which egg yolk is added as a binder instead of gum arabic. These colors are unlike watercolor paints, with a slightly more oily appearance, and they dry faster.

A third, quite popular type of color, which is often seen on black-and-white photos, is black India ink. We can use pre-diluted ink or powder. Of course, also in this case, we use only high-quality inks from the best manufacturers, which print in completely black color and are not overly absorbed in the paper.

In recent years, more and more enthusiasts of gum printing use acrylic paints of good quality made by well-known manufacturers, in place of a variety of watercolors. Although we cannot know whether these colors are really as persistent as the watercolor of cave paintings or tempera from ancient Egypt, almost all manufacturers guarantee their stability.

About pigments

As we mentioned earlier, paints used in gum printing must meet certain requirements, and to understand these we need to know some of the basic properties of pigments. We will mention only three of the most important properties for us, which producers of better paints always describe on their product labels or color charts of pigments.

Permanence or lightfastness

Some colors lose intensity in the saturation of light over time, while others, such as some yellow colors, darken, and some lighten, etc… Permanence of colors, sometimes also called lightfastness, is most commonly graded by a number of stars, and producers measure it by prescribed standard tests. For example, five stars indicates absolutely stable color, and one star indicates completely unstable pigment. On the products of other manufactures, we see markings like AA, A, B and C, with AA indicating a fully-permanent color and C a completely unstable color. A third manufacturers’ grading is indicated with three stars for a complete resistance, and the like.

Colors whose properties are not altered over a period of 100 years in a museum environment are considered “very permanent.” “Less resistant” colors are expected to be those which, in the aforementioned conditions, change in 25 to 100 years. “Unstable” colors change in appearance in less than 20 years.

For permanent gum print, we will, of course, choose only the most permanent color, because we don’t want our photo to completely disappear after just a few years.

Transparency

For gum prints, the transparency of colors is also very important, as non-transparent colors, when mixed with a small amount of gum arabic, can completely cover an image on pre-made layers. This property is particularly important when printing color photographs, which we will learn about in a separate book on color gum printing.

The color industry manufacturers most frequently mention 4 levels of transparency: transparent, semi-transparent, semi-opaque and opaque. Each manufacturer indicates that property with a variety of symbols, most often with triangles, squares, or circles.

Staining

In the industry of colors, we will most frequently notice three descriptions of staining: non-staining, semi-staining, and staining, whereby of course colors labeled as non-staining are the best to use, because these colors can easily be washed out of the paper. In the case where we use color with a greater power of staining, we will lose all the bright tones, despite prolonged washing in water and despite good sizing.

Gum Print

Washing of colors in gum printing is also affected by the quality of the gum arabic, which is used in the manufacture of paints as a binder agent of pigment and prevents the pigment from being absorbed into the paper. Of course, we will find very high-quality gum arabic only in professional colors, since manufacturers most commonly use Polyethylene glycol (PEG), which is a kind of artificial replacement of gum arabic, in the colors of lesser quality.

Copyright © 2016 Peter Mrhar.