Casein Pigment Prints, known as the casein bichromate printing process, utilizes curdled milk dissolved in ammonia to bind the component materials and was patented in various forms starting in the 1870s, as a technique to use with other photo-printmaking methods, such as over Van Dyke brown printing and cyanotype. One of the least expensive of the hand-applied emulsions, casein printing is closely related to gum bichromate printing, and a reading of that chapter is highly recommended. Casein usually requires much less ultraviolet exposure to yield stronger and slightly more distinct colors than the gum bichromate process. Bichromate can cause skin and eye irritations and even burns upon repeated exposure. Bichromates can be poisonous when ingested, even in small quantities, so keep containers labeled, and store chemically contaminated materials away from the mouth and out of the reach of children and pets. Bichromate is carcinogenic to humans after long-term or repeated exposure, and it may cause asthma.