Patented in 1841 by William Henry Fox Talbot, the calotype (Talbotype) became the basis for all subsequent negative/positive processes. Thanks to the research of Sir John Herschel, the calotype was the first process to utilize sodium thiosulfate as a permanent fixer for the image. Silver nitrate, potassium iodide, and gallic acid are among additional ingredients you will need. Strictly speaking, calotypes refer to the negatives the process yields. However, the name is sometimes attributed to the positive print made from the negative, historically the salted-paper print.