Photogenic drawings were prepared by soaking a piece of good quality drawing paper in a weak solution of common salt, allowing this paper to dry, brushing it with a solution of silver nitrate, and then further washing it in a strong solution of common salt. Exposure was usually made by contact printing for as long as it took an image to appear. This image would then be fixed: Talbot used a strong solution of common salt for this or, occasionally, potassium iodide; Herschel's hypo fixer (sodium thiosulphate) dissolved away any remaining silver nitrate more efficiently and subsequently became the standard for all silver processes.