The first widely used photographic process in which images could be produced on paper. Writing paper is prepared with solutions of silver nitrate and then potassium iodide. When required for use, it is treated with a freshly prepared solution of gallo-nitrate of silver. It is then exposed and the image is brought out by a further treatment with gallo-nitrate of silver and fixed with hypo. It was invented by the English scientist William Henry Fox Talbot in 1839, patented in 1841, and was also know as Talbotype.