They result in an photo-sensitive solution when solved in water, which is used to coat a material (usually paper). A positive image can be produced by exposing it to a source of Ultraviolet light (such as sunlight) with a negative.
The developing of the picture takes place by flushing it with flowing water. The water-soluble Iron (II) salts are washed away, while the non-water-soluble Iron (III) salt crystals remain in the paper. These are which give the picture its typical blue color. 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, the so-called blueprint.
Long term preservation:
In contrast to most historical and present-day processes, cyanotype prints do not like basic environments. So it is not a good idea to store or present the print in chemically buffered Photographic processes
