The cyanotype process was widely used from the late C19 as an efficient early method of making copies known as 'blueprints'. It enabled the reproduction of technical and engineering drawings before photocopiers. Prints are made by coating paper with a light-sensitive emulsion and placing it under the original drawing to be copied. The stack is then exposed to UV light; the inked lines block the light and remain white while the exposed areas turn blue. This is a detail of a blueprint design for typically elegant lettering and numbers (1890) by CFA Voysey in the RIBA collection.