• A piece of
paper, usually 100% cotton, is coated with an emulsion of egg white (albumen) and salt (
sodium chloride or
ammonium chloride), then dried. The albumen seals the paper and creates a slightly glossy surface for the
sensitizer to rest on. • The paper is then dipped in a solution of
silver nitrate and water, which renders the surface sensitive to UV light. • The paper is then dried in the absence of UV light. • The dried, prepared paper is placed in a frame in direct contact under a negative. The negative is traditionally a glass negative with
collodion emulsion, but this step can be performed with a modern
silver halide negative, too. The paper with the negative is then exposed to light until the image achieves the desired level of darkness, which is typically a little lighter than the end product. The progress of the print can be checked during the exposure, as it is a printing-out process, and the image can be seen taking form as it is being exposed to light. Though direct sunlight was used long ago, a UV exposure unit is often used contemporarily because it is more predictable, as the paper is most sensitive to
ultraviolet light. • A bath of
sodium thiosulfate fixes the print's exposure, preventing further darkening. • Optional
gold or
selenium toning improves the photograph's tone and stabilizes against fading. Depending on the toner, toning may be performed before or after fixing the print. Because the image emerges as a direct result of exposure to light, without the aid of a developing solution, an albumen print may be said to be a
printed rather than a developed photograph. The table salt (sodium chloride) in the albumen emulsion forms silver chloride when in contact with silver nitrate. Silver chloride is unstable when exposed to light, which makes it decompose into silver and chlorine. The silver ion (Ag+) is reduced to silver (Ag) by the addition of an electron during the development/printing process, and the remaining silver chloride is washed out during fixing. The black parts of the image are formed by metallic silver (Ag). ==References==