GUM BICHROMATE PROCESS PDF
Terry King gives an overview of gum bichromate printing, along with a step-by- step guide to the process. Fifteen years ago, I was in a similar. Gum bichromate process definition, a contact printing method in which the image is formed on a coating of sensitized gum containing a suitable colored pigment. In the late s, pictorialist photographers favored a diversity of photographic techniques, including the gum dichromate process. Sometimes superimposed.
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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.
Should you choose a very strong UV source, a weaker solution may offer better control of your exposures. They are not exclusive. Bichomate Henry Fox Talbot later found that colloids such as gelatin and gum arabic became insoluble in water after exposure to light. Try to start with negatives that have good not necessarily high contrast and density. It is not unusual to use a small brush to help bichromae away small areas of unwanted pigment.
A staining pigment will stain the whole of the image area. The Museum cannot endorse or accept responsibility for the service offered by any supplier. The print was then watercolored while still damp. I would suggest that you bicromate your exposure time, perhaps even triple the time. Your email address will not be published. Afterwards, the print is hung to dry.
Hello Terry, Thank you for your inquiry. The more pigment you use the less chance the light has to do its work. Witness, too, the plethora of new publications devoted to the subject of gum printing and the increasing number bichromwte exhibitions featuring both monochrome and tricolor prints. By Terry King on 5 May Introduction to gum bichromate printing. By how you describe the results of your prints, you have underexposed your images.
The variables become more manageable while the image quality is virtually identical. Some photographers prefer substituting the cyan emulsion in the CMYK separations with a cyanotype layer. I, for my part, went to a talk by a gentleman from Maidenhead called Steinbock. Gum bichromate, or gum dichromate as it is also known, is a photographic printing process invented in the early days of photography when, inMungo Ponton discovered that dichromates are light sensitive.
This stiffens the chain and the resulting stiff gum becomes insoluble in bichrpmate. The print is then floated face down in a bath of room-temperature water to allow the soluble gum, excess dichromate, and pigment bichrimate wash away. There are probably no two prkcess printers who approach their work in precisely the same manner.
Therefore, begin experimenting with watercolor papers that can handle repeated washes. In a separate tray, gently run cool water for 10—20 minutes with the print face down to remove all metabisulphite solution. My preference favors a potassium solution.
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.
An introduction to the gum bichromate process
A simple duotone separation combining orange watercolor pigment and a cyanotype can yield surprisingly beautiful results. The ammonium compound is three times as nasty and three times as fast.
Make lots of sized paper at one time. Each layer must be fully processed and dried before subsequent layers can be applied.
Paper Most papers, and for that matter most surfaces that are not smooth and shiny, can be used for gum printing. A good print begins with a good negative. Use medium speed camera film either direct from the camera or enlarged onto the baseboard from a transparency.
You may or may not feel the effects of overexposure, but know that you are being overexposed if drying with a hair dryer. 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. I developed the film in dilute Dektol 1: Gelatine is a very effective size and one that many gum printers continue to use today with excellent results.
A gelatin size coating prevents the unhardened dichromate from permeating the paper fibers. Low density photographic negatives of the same size as the final image are used for exposing the print. Remember-mix thoroughly and occasionally stir as you use it! The information provided below is just one of many points of embarkment and offered to the reader as basic introductory material.
Gum Bichromate Process | NINIANE KELLEY PHOTOGRAPHY
It is good for your first experiments. This can be seen bichromzte the reverse of the paper as a yellow stain where pigment was applied on the verso.
Insert into your contact printer or sandwich with your plate glass see step three in the Cyanotype process.
One would think gum printing has, at last, come of age. Brushes The gum bichromate emulsion is essentially a modified watercolor. Gloy gum is PVA with surfactants; it is three times as fast but not so easily controlled.