'So cyanotypes are cameraless photographs made when an object - a botanical specimen, a feather, a bit of lace - is placed under glass on chemically treated paper and left in the sun. When the object is removed and the sheet washed down, a ghost shadow remains where the light hasn't touched the paper. This process was  later adopted by architects to reproduce their drawings. It's where the term "blueprint' comes from. And it was the inspiration of Anna Atkins' (the New Statesman here).