Sun printing may refer to various printing techniques which use sunlight as a developing or fixative agent.

Cyanotype

Cyanotype

Cyanotype

Cyanotype is a photographic printing process that gives a cyan-blue print. The process was popular in engineering circles well into the 20th century. The simple and low-cost process enabled them to produce large-scale copies of their work, referred to as blueprints...

, also referred to as "blueprinting", is the oldest non-silver photographic printing process. It involves exposing materials which have been treated with a solution of potassium ferricyanide

Potassium ferricyanide

Potassium ferricyanide is the chemical compound with the formula K3[Fe6]. This bright red salt contains the octahedrally coordinated [Fe6]3− ion. It is soluble in water and its solution shows some green-yellow fluorescence.-Preparation:...

 and ferric ammonium citrate to a UV light source such as the sun. Negative or positive images can be obtained by blocking UV light from reaching the sensitized material. For example, a negative image can be produced by placing a leaf upon paper treated with this solution and exposing to sunlight for 10 to 20 minutes. The paper will retain the image of the leaf after it has been rinsed with water. Once the paper dries, parts that were exposed to the sun will turn a shade of Prussian blue (ferric ferrocyanide)

Prussian blue

Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....

, while parts that were covered by the leaf will remain white.

Light-sensitive vat dyes

A specialized type of vat dye

Vat dye

Vat dyes are an ancient class of dyes, based on the natural dye, indigo, which is now produced synthetically.-Overview:The process "vat dyeing" refers to dyeing in a bucket or vat. It can be performed whenever a liquid, even shade over the entire garment is desired. Almost any dye can be used,...

 called Inkodye is also used for sun-printing due to its light-sensitive quality. Unlike other vat dyes which use oxygen to develop their color, Inkodyes are developed by light. These dyes are suspended in leuco form

Leuco dye

A leuco dye is a dye whose molecules can acquire two forms, one of which is colorless.For example, the spiro form of an oxazine is a colorless leuco dye; the conjugated system of the oxazine and another aromatic part of the molecule is separated by an sp3-hybridized "spiro" carbon...

 appearing colorless until they are exposed to UV. Their usage resembles that of cyanotype, but unlike cyanotype Inkodyes are primarily used on textiles and exist in a full range of colors. Exposure times vary from 3 to 15 minutes depending on the desired color and intensity of light. Once exposed, the sensitized material is washed in soapy water to remove dye from unexposed areas. Such dyes are typically used by craftspeople, fabric printers and artists and can be printed with photographic negatives

Negative (photography)

In photography, a negative may refer to three different things, although they are all related.-A negative:Film for 35 mm cameras comes in long narrow strips of chemical-coated plastic or cellulose acetate. As each image is captured by the camera onto the film strip, the film strip advances so that...

, resist paste

Resist dyeing

Resist dyeing is a term for a number of traditional methods of dyeing textiles with patterns. Methods are used to "resist" or prevent the dye from reaching all the cloth, thereby creating a pattern and ground. The most common forms use wax, some type of paste, or a mechanical resist that...

 or through a silk screen.

Potassium dichromate

Sun printing may also refer to a photographic process using potassium dichromate which produces a negative plate for conventional lithographic printing

Lithography

Lithography is a method for printing using a stone or a metal plate with a completely smooth surface...

. The process uses a film of gelatine spread on a flat and rigid surface. This is coated with a dilute solution of potassium dichromate and dried in low light conditions. A translucent positive is secured in tight contact with the treated gelatine layer and exposed to bright sunlight for a period of up to 30 minutes. During this time the sunlight and potassium dichromate tan the gelatine exposed to light. The plate is developed by washing in warm water and removing the untanned gelatine. Once dry, a relief print

Relief print

A relief print is an image created by a printmaking process where protruding surface faces of the matrix are inked; recessed areas are ink free. Printing the image is therefore a relatively simple matter of inking the face of the matrix and bringing it in firm contact with the paper...

 is revealed on the plate. The surface can be ink

Ink

Ink is a liquid or paste that contains pigments and/or dyes and is used to color a surface to produce an image, text, or design. Ink is used for drawing and/or writing with a pen, brush, or quill...

ed and printed in a hand press to produce any number of identical prints of the original subject.

External links

• Inkodye - Light-sensitive vat dyes