he Calotype was a positive/negative process introduced in 1841 by Fox Talbot, and popular
for the next ten years or so. Strictly speaking the term refers only to the negative image,
but it is commonly taken to mean both.

A piece of paper was brushed with weak salt solution, dried, then brushed with a weak
silver nitrate solution, dried, making silver chloride in the paper. This made it sensitive to light,
and the paper was now ready for exposure. This might take half an hour, giving a print-out
image. It was fixed in strong salt solution - potassium iodide of hypo.