I'm studying calotypes and cyanotypes.

Their major contribution to the development of photography was the fact that they could be easily copied. The original negative could be used to create as many positive copies as wanted, with a process called contact printing.

However for contact printing to work as desired, the original negative had to be translucent. I don't understand how it was made translucent.
From Wikipedia,

Talbot made his first successful camera photographs in 1835 using paper sensitised with silver chloride, which darkened in proportion to its exposure to light......In late 1840, Talbot worked out a very different developing-out process, in which only an extremely faint or completely invisible latent image had to be produced in the camera, which could be done in a minute or two if the subject was in bright sunlight....The light-sensitive silver halide in calotype paper was silver iodide, created by the reaction of silver nitrate with potassium iodide...... The calotype process produced a translucent original negative image from which multiple positives could be made by simple contact printing.

I don't get if the paper initially used it's itself translucent or it's a developing process that makes it translucent.

  • Are you confusing translucent with transparent? – Mike Dixon Dec 11 '17 at 15:11
  • @MikeDixon I haven't the physics background to tell what difference would make using a transparent negative instead of a translucent one....I just know that translucent objects allow all light to pass while translucent only a part. But as stated from sources, translucent negatives seem to be used. – Gabriele Scarlatti Dec 11 '17 at 15:23

Talbot bathed paper sheets in a solution of silver nitrate and then potassium iodide. He then “washed” the paper with a mix of gallic acid and silver nitrate. The paper was then exposed in the camera. The exposed paper was bathed again in this wash solution he called “gallo-nitrate of silver”. He then fixed the image (rendered permanent), with a hot solution of hypo (sodium thiosulfate) (Patent # 8842 Feb 8th 1841. The pictures were printed (converted to positives) by his wife. The print paper was sensitized with silver chloride. This sensitized paper was placed in a frame. This sandwiched the print-out paper under the paper negative, while a cover glass kept all in contact. The frame was taken out into the sunlight. The exposures ranged from a few minutes to an hour or more. It took brilliant sunlight to penetrate through the negative and expose the print paper. A visible image was formed -- no need to develop. This image was fixed, washed and dried.

  • This is interesting, but what about the specific question of translucency? – mattdm Dec 11 '17 at 15:07
  • As much as I appreciate your answer, it doesn't address the question – Gabriele Scarlatti Dec 11 '17 at 15:25
  • @ Gabriele Scarlatti - The negative image is on paper. While paper is not as transparent as a modern negative, an image on paper can be seen by transmitted light. It is this transmitted light produced by bright sunlight that exposes the print paper under the negative. Latter the transparency of the negative was improved using waxed paper. – Alan Marcus Dec 11 '17 at 15:59
  • Do you know of the composition of the early papers used and how they would differ from, say, modern printer paper or card stock? (attempting to get a frame of reference for the translucence of those early papers) – Hueco Dec 11 '17 at 16:38
  • 1
    @Corey they would have been a lot thinner than card stock (which technically is paperboard). Probably thinner than most printer or notebook paper. Keep in mind that we are talking about monochromatic images here. If you place an opaque object behind a piece of paper and shine a light through it from behind you can easily see the outline of the object. The various density of the different parts of the negative allowed more or less light through. The constant density of the paper attenuated all areas equally. The differences in each area were still the same as the differences in the negative. – Michael C Dec 11 '17 at 19:30

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