Old Photography Process: Calotype
Calotype (Greek: kalos – “beautiful”, and tupos – “impression”), sometimes called Talbotype, by its inventor Henry Fox Talbot, with slight differences than the process as we now know it, was introduced in the autumn 1840, and patented in February of 1841. It’s an early photographic technique where paper is coated with silver iodide. It was offered as cheaper and simpler alternative to Daguerreotype and was widely accepted among both photographers and amateurs, but it failed to replace it completely.
While Daguerreotype was still more popular in 19th century, for its sharp lines and clear images many photographers worked with calotypes exclusively, because it gave softer look to images. Calotype can be compared to drawings with charcoal, so it is, even nowadays popular for those who want picturesque images of nature, buildings and still life.
The main advantage over daguerreotype is that calotype produces translucent original negative that can be used multiple times, giving positive by simple contact printing.
The light sensitive layer on high quality paper is silver iodide, created by the reaction of silver nitrate with potassium iodide. First stage in calotype process demands preparation of the paper (paper should be smooth, with uniform texture and without watermark) where it’s being washed over with a solution of silver nitrate and dried by gentle heat then dipped it in a solution of potassium iodide for two to three minutes, rinsed then dried again. Paper that has been prepared this way was insensitive to light, and it could be stored for some time, if handled properly, so it was generally prepared in batches before the actual exposure.
When wanted for use, the side of paper that has been brushed with silver nitrate is dipped in a fresh solution of gallo-nitrate of silver. This was made from equal quantities of silver nitrate and one of gallic acid and considering the fact that this solution was very unstable, it had to be used right away. Under a weak light (usually a candlelight or something equally weak), paper was dipped in a solution for about half a minute and later washed in water. It could be used when completely dry, but gave better results if used moist. In any case, paper had to be used within couple of hours.
In a total darkness (or again, under a weak light, near-total darkness), paper was loaded in camera. These cameras, though wooden and large, could easily relate to modern film cameras.
Exposure of material took sometimes just a couple of seconds, but more often up to couple of minutes, usually just about a minute. Image is, at this point invisible and it is dipped in fresh solution of gallo-nitrate of silver, while the paper is gently warmed. When development was complete by the opinion of the photographer, the calotype was rinsed, blotted, and then fixed with liquid. The fixer used can be either a solution of potassium bromide or a solution of hypo (which is very similar to modern fixers). Later comes the rinsing and drying of paper.
Image was at this point the negative on a high quality paper, deep brown or black in color. Strictly speaking, the term calotype referred only to the developed negative process. Prints could be made on the calotype paper, prepared exactly like we explained, exposed and then developed much like modern photographic papers, but this was done rarely (only just a couple of times) because it was complicated and took time, while the results in tones were mostly unsatisfactory. What was used instead was Talbot’s originally invented photogenic drawing paper.