GUM BICHROMATE PROCESS PDF

Fifteen years ago, I was in a similar state of mind to that of Robert Demarchy some ninety years before. I too needed something to enliven my personal photography. Someone suggested to Demarchy that he should go back to the experiments of the s. This was when alternatives were being sought to the impermanent silver photograph. Demarchy found his inspiration in the gum print and went on to become one of the leaders of the Pictorial movement, a movement which later was to become both derided and degraded.

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Fifteen years ago, I was in a similar state of mind to that of Robert Demarchy some ninety years before. I too needed something to enliven my personal photography. Someone suggested to Demarchy that he should go back to the experiments of the s. This was when alternatives were being sought to the impermanent silver photograph.

Demarchy found his inspiration in the gum print and went on to become one of the leaders of the Pictorial movement, a movement which later was to become both derided and degraded. I, for my part, went to a talk by a gentleman from Maidenhead called Steinbock. He showed me my first gum print. But the technique of this black and white print gave it a power, a hyper-reality that seemed to outshine so many of the silver gelatin prints I had seen.

My immediate reaction was that, if he could do that in black and white, there must be a whole new world out there, in colours, that I could choose for myself. Subsequent experience showed that after cyanotype, using a contrasty negative to make a gum print is the easiest way to make a photograph. And if that is the peak of your ambition, then fine. But, as with the cyanotype, if you want any subtlety, you will need to apply photographic expertise and experience.

In the case of the gum print you will need it by the ton. Also, to rise to the challenge of the process, you will need to be bull-headed and persistent as there are so many variables and so much that can go wrong.

That was a health warning. But the end result of your persistence can be so exciting, and give you so much freedom from the parameters laid down by the chemists, that silver gelatin will seem to lack lustre, and the only two other photographic printing methods that will seem worthy of serious attention will be platinum and gravure. One of the joys of the gum process is that there is no one right way of doing it.

The method you establish will reflect your own personality and way of working. But do not try it if you are tense or in a bad mood. If you are the kind of person who needs to be told precisely what to do, you have probably given up reading this already. What I intend to do is give the recipe, details of the materials and their sources, the basic working method and a few useful hints.

It is then up to you to go away and make your gum print. Put in terms that I can understand, the gum molecule is a flexible chain of hydrogen and carbon atoms with oxygen side spurs. The dichromate molecule can be excited by light at the right wavelength to throw one of its oxygen atoms which fills in the gaps between the spurs on the gum molecule chain. This stiffens the chain and the resulting stiff gum becomes insoluble in water. Increasing the levels of light or dichromate, increases the insolubility of the materials which consequently, lessens the contrast.

After exposure and development, the insolubilised gum, which is porous, retains the solid particles of pigment, while any remaining dichromate in solution is washed away. Well, that was fairly simple; remembering these principles should enable you to answer most of the problems that the process throws up. Method For a monochrome or multicolour three exposure 16 x 12 print, to obtain a wide range of tones.

Squeeze a pea-sized amount of pigment onto your tea plate, and add 5cc of gum and mix thoroughly using palette knife. Add 5cc of saturated dichromate solution and mix thoroughly. Tape down paper to a smooth surface and mark off area to be covered by negative. Coat paper with a lightly dampened brush using smooth caressing strokes, being sure not to abrade the surface.

This may be done in subdued light. Your objective is an even surface. Place in the dark to dry for at least forty minutes until there is no trace of tackiness or shine on the surface. Remember that the chemical reaction is only speeded up by light. It continues in the dark to the extent that you should not be surprised if results from sensitised paper stored for more than twelve hours prove unsatisfactory.

I am told that it will last longer if you store the paper in the freezer. Place the negative, emulsion side up, on the sensitised paper. Tape it down outside the picture area and make two holes through the margin of both the negative and the paper using the map pins. These holes will serve for registration for subsequent exposures. Your first exposure should be between five and fifteen minutes depending on the negative. Tests are advisable. If you are using pigments other than strong blacks, the image should print out.

If it does not look as if it is done enough, give it a bit longer. Develop in lukewarm water to wash away the uninsolubilised gum to the desired level of contrast. Floating the print upside down on the surface of the water is known as automatic development.

You have to wait until you can see the pigment falling off. Using a wet soft brush gives you greater control as does directing streams of water at those parts of the print you wish to affect. Remember one extra minute under the lamp means ten extra minutes of development. You are developing for detail in the highlight areas; do not attempt to make this first exposure look like a finished print. Dry in a strong stream of warm air. If you have significant areas of highlight, size.

Recoat, using more pigment, for the middle range of tones, then repeat steps 3 through 8, but the exposure should be one third of that at 6, or less. Repeat using more pigment and a shorter exposure for the shadow detail. Dry, fix in UV light for a short time, and wash for six hours. If you are impatient to see the final colours uncontaminated by the orange of the chrome salts, place the print in a clearing bath of potassium metabisulphite.

The stronger the solution, the quicker the clearing. I just use water. There are many other ways of making a gum print. Some are more complicated and achieve different aesthetic results. Others satisfy the need of the proponents for complication. Other methods depend upon cumulative misreadings and misunderstandings of writers on the subject for the past years.

I reinvented the process for myself to keep it simple and avoid deadly poisons such as mercuric chloride which some use to kill off the bugs in the gum. There seems to be as much chance of killing yourself. Make fresh as you go along. For me, the picture is the objective, not the process. They are cancer suspect agents. As with all chemicals, treat them with respect. Potassium dichromate K2Cr can be dissolved to the extent of one part in eleven in water.

Ammonium dichromate NH4Cr can be dissolved to the extent of one part in three in water. This is the maximum amount that can be absorbed and is known as a saturated solution. The ammonium compound is three times as nasty and three times as fast. Light You need near ultra violet light x m available free from the sun but inconsistent. Alternatives are blacklight fluorescent tubes or mercury vapour UV graphic art lamps which offer greater flexibility.

UV health lamps also work. Brushes You will be spreading gum, which watercolourists use as a lacquer, onto watercolour paper. The recommended brush is a watercolour lacquer brush; Omega, series 40 with a code number that gives the width in mm. Gum Gum arabic comes from a tropical acacia tree.

Winsor and Newton sell it in a prepared form that is expensive but is of the right consistency Beaurme. It is good for your first experiments.

You can buy a very expensive version in lumps, together with bits of tree, which is known as royal gum arabic. White gum arabic powder, diluted with cold water and left to dissolve, achieves much the same effect. Liquid gum sold as an etching resist is too thin. Gloy gum is PVA with surfactants; it is three times as fast but not so easily controlled. Paper Most papers, and for that matter most surfaces that are not smooth and shiny, can be used for gum printing.

Paper below gsm in weight will need stretching by taping it to a smooth surface around the edges of the paper and then soaking it so that as it dries, it shrinks and stretches. I avoid problems of sizing and lack of lateral stability by using papers that are adequately sized and of adequate weight.

They also have a tooth to hold the gum to the surface during development without a tooth, your picture will fall off the paper as the light acts upon the surface of the emulsion. Both papers are PH neutral and archivally sound. They are Bockingford lb and Fabriano 5 Not gsm.

The more pigment you use the less chance the light has to do its work. A basic palette should include red, alizarin crimson; blue, cobalt and indigo; yellow, new gamboge; green, sap green; burnt sienna for brown and neutral tint and ivory black. Avoid pigments that stain such as the Hookers greens. You will be coating the whole of the paper and washing away the gum you do not want. A staining pigment will stain the whole of the image area. Film The gum emulsion is very slow and is only capable of accepting a density range of about 0.

You will need to make contact prints and give more than one exposure if you wish to obtain a wide range of tones with good gradation.

FR302 DATASHEET PDF

Gum Bichromate

Coat with sponge brush in low incandescent light Dry in dark or nearly dark Printing in one color[ edit ] coat and dry several sheets of paper, choose a softly lit image with strong tonal gradation. Place intermediate negative with sensitized paper clamp down with a piece of glass. Test exposures, 30 secs to 2 minutes with film negatives paper negatives take several hours. Cover paper in cold water face down until orange dichromate and gum pigment diffuses out. Choose the time that produces the best results and expose a second sheet, and start again with best exposure time. After processing full print, brush away unwanted shadows with a small soft water color brush Tape print to board and let dry Printing in three colors[ edit ] Make three color separations blue, green, and red filters use panchromatic film Mix three pigmented gum solutions yellow, magenta, and cyan add sensitizer before applying each to the paper Coat with sensitized yellow gum and expose to the blue separation. Process and dry, recoat with magenta gum to print to the green separation.

DYNALITE PHILIPS PDF

An introduction to the gum bichromate process

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