COATING PAPER AND OTHER MATERIALS
Application of cyanotype, Van Dyke Brown, and gum bichromatic solutions can be carried out in any way which achieves the desired result. A good quality hair brush with soft bristles may be used for an even coating, or cheaper brushes can be used to reveal the kinds of marks the brush can make. A cotton swab, or aerosol spray may be used for the kinds of marks that they will make. Paper or material can be floated directly in a tray of the solution (though this requires a lot of solution). Be careful however,when using this technique with absorbent material for it will soak up enormous amounts of solution. When coating fabrics, they can be soaked and wrung out, but please wear protective gloves.
Since the paper is sensitive to light only in the coated areas, you could consider coating areas selectively, in relation to the formation of image and page design. A variety of materials can be employed as masking devices and stencils to hold back the light or partially expose the image areas.
All solutions can be applied over drawings in pastel or permanent ink, or already printed materials like maps or book pages or printed fabrics.
Heavily sized papers are not recommended for blue and brown printing as they will repel the solutions. Arches, Rives, some rice papers, vellums, and tracing papers work well. Test any paper that interests you by placing it in running water for about 5 minutes. If the paper fibers rise or separate too much, you will likely have difficulties.
Cotton fabrics work well for blue and brown printing, and may be used sized or unsized. Avoid synthetics and very heavily sized materials. Regular laundry or spray starch will work well as a size for materials that are too absorbent. Washed cotton bedsheets are excellent for printing.
The solutions can be applied much the same as for papers. Apply with a brush or by floatation. To avoid brush marks, try applying solutions with a sponge or sponge brush. If you are coating several pieces of fabric, stack them on top of each other and allow the solution to absorb from one piece to the next. This will prevent waste of solution.
Blue, brown, and gum bichromate solutions are not extremely sensitive to light until they have dried. This allows you to prepare the paper in fairly light situations. Subdued room light or a commercial bug lamp will do.
Papers should dry face up on a clean screen or surface, or hanging vertically. For absorbant materials such as cloth, hang to dry and ventilate with a fan. Forced drying with a hair dryer works fine as long as the coated surfaces are not heated too much.
Most hand-applied emulsions are most effective if they are exposed when they are just dry. Waiting too long to expose after drying will usually result in loss of sensitivity, hardening of the emulsion, and staining.