An extract from Sarah’s book A Non-Silver Manual, which is available for free.
The non-silver processes covered in A Non-Silver Manual rely primarily on the energy of light rather than the energy of chemicals to produce a print. This light, referred to as actinic light, is rich in ultraviolet and blue rays. In the 19th century the only source of actinic light was the sun. Where actinic light strikes paper coated with one of the non-silver solutions or emulsions for a sufficiently long time, a chemical reaction occurs and the coated paper darkens or takes on a different color. Where actinic light is prevented from reaching sensitized paper, the chemicals wash out leaving plain paper. Where light is partially prevented from striking, a tone is produced that is somewhere between the completely darkened paper and the original color of the paper.
The ways of making light-resists discussed below produce white shapes or marks on a dark ground – with the exception of “Opening Up Line”.
3-D Photograms: The most direct way to produce an image is to lay objects upon the sensitized paper. This is a variety of photogram. A point light source, such as the sun in a clear sky or an old-fashioned sunlamp, casts shadows from standing objects that print clearly. A diffuse light source, such as an overcast sky or an array of black light tubes, eliminates delineating shadows revealing only the “footprint” of the object on the paper.
Partially translucent objects allow varying amounts of light to penetrate to the sensitized paper and produce intermediate tones.
Such tones can be produced also by moving opaque objects during the exposure.
Flat Photograms: Materials that can be pressed tight by plate glass against sensitized paper – such as botanical specimens, tissue, wisps of cotton, locks of hair, lace, onion skin, cheesecloth, and translucent printed matter – produce light shapes in various tones on a dark ground. If you want to prevent chemical reactions or staining, insert a layer of clear acetate between the coated paper and damp photogram materials such as leaves or flowers. You could tape or glue photogram materials to the acetate to permit multiple printings of a particular arrangement of photogram materials. You could also compose a number of related photograms on acetate to print in successive layers of gum bichromate colors or layers of other non-silver processes.
Markers, Washes & Colored Pencils: The same clear acetate may be drawn on with rubylith or amberlith AD markers. Red and orange dyes in these markers block actinic rays. The inks in other markers, such as black, brown or red Sharpies, are not designed to hold back light very effectively. Blue and green markers definitely allow actinic light to penetrate and are the least effective light resists.
In 2001, Faber-Castell introduced Pitt Artists Pens in black, sepia and sanguine – all permanent, acid-free India inks that do block light effectively. Each of the three colors comes with 4 different nibs including a versatile brush nib. Artist Mary Laniel Nakigan used the 3 colors to draw registered acetate separations to print in 3 gum colors with great success. Now, in 2005, Pitt Pens are available in a wide range of colors which could be used to block varying amounts of light.
Photo opaque, acrylic paint, and various inks and watercolors can be strong light-resists when used full-strength but washes of these materials diluted with water bead up on the slippery surface of regular clear acetate. Rosae Reeder recently told me that you can add a drop of a surfactant such as Photo-Flo or even liquid detergent to reduce surface tension and allow such materials to adhere. There are also certain more expensive clear acetates that are treated to accept washes. Frosted acetate, frosted mylar, and tracing paper will accept washes in photo opaque, Plaka, Pro-Color, and acrylic paint. (Unfortunately photo opaque and Plaka are no longer easy to obtain. Plaka is being discontinued for “health reasons” – perhaps the ammonia fumes from its casein base.) Inks and watercolors can be tried on frosted acetate or mylar, perhaps with a drop of a surfactant, but with no guarantees. Tracing papers, especially sturdy vellums, tend to take washes easily but their density prolongs exposure time onto papers sensitized with non-silver processes, especially when printing in relatively slow cyanotype. Graphite, crayons, and colored pencils in the black-sepia-sanguine-orange range can be used on the frosted materials and on tracing paper or vellum for light-resists.
If dark figures on a white ground are desired, a contact negative must be made (unless you have been clever enough to draw a negative). A contact negative can be made in a darkroom by placing the photogram object(s) or drawing in contact with sheet film or photographic paper, exposing and developing it appropriately, and then using the resultant “negative” to produce a positive non-silver image.
Opening Up Lines: Sheets of rubylith or amberlith masking film can be used to create high-contrast light-resists. Film-cutting tools provide an easy way to open up lines on masking films that will then print dark on a white ground.
If you should accidentally fog a sheet of black-and-white film, don’t throw it away. Instead, expose it completely to daylight or artificial white light, develop, stop, and then wash it-no fixing should be necessary because there is no unexposed silver salt to dissolve out. The resultant black sheet can be scratched on the duller emulsion side with a sharp tool such as an etching needle. Dampening the emulsion side of the film with a sponge or paper towel allows smoother removal of the metallic silver by scratching and even permits a degree of tonal gradation with a tool as primitive as your fingernail. You may want to try this on actual negatives too. Scratching on the film can be a bold way of saving an overexposed or fogged pinhole negative or copy camera negative.
Cliché-verre is a late 19th century ancestor of the scratched films described above. A group of French artists, referred to as the Barbizon School, that included Corot and Millet, worked directly from nature and made drawings with etching needles on opaqued glass that they printed in gum bichromate and other processes. The resultant images, resembling etchings, were called cliché-verres (repeatable glass prints). Traditionally, glass was opaqued by holding it over a lantern and allowing soot to darken it, or by brushing brown hard-ground (used on etching plates) onto the glass. Today some printmakers still use hard-ground but various modern water-soluble materials seem to work even better because they don’t offset on the printing paper, melt under hot lights, or involve the use of solvents. It is not necessary to opaque an entire sheet of glass; it can be coated partially or in painterly brush strokes. Some of my students have included photographic negatives upon the glass, opening opaqued areas with a single-edge razor and attaching the film to the coated side with a few drops of gum arabic that can be washed off the film later. To obtain a sharp image a cliché-verre must be printed with the drawn side in contact with the sensitized paper. (This means that your image and text will be laterally reversed.) Otherwise, light will spread as it passes through the thickness of the glass and the image will be blurred. Of course a softened image is preferable sometimes. One could draw with a focal plane in mind on one side of the glass and then draw on the other side in lines and shapes that will print out of focus. As is the case with etchings, cliché-verre plates can be reworked, filling in some areas and opening up others to produce different “states” of the image. These states can be printed in different layers of non-silver processes if desired.