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Document number: 09097
Date: 08 Mar 1839
Dating: date confirmed by Traherne's note
Recipient: TALBOT William Henry Fox
Author: JONES Calvert Richard
Collection: British Library, London, Manuscripts - Fox Talbot Collection
Collection number historic: LA39-19
Last updated: 31st July 2012

[this querry was conveyed by Traherne's note - see Doc. No: 03834].

8th March 1839

The exact proportion between the salt and water, and between the nitrate of silver and water which he considers best.<1>

And the time between repeating the washings which produces the greatest sensibility.<2>

Calvert R. Jones

Notes:

1. WHFT's photogenic drawing utilised silver choride as the light-senstive agent. However, this was insoluble in water, making it impossible to coat onto the paper, and necessitating a two-step process. First the plain writing paper was brushed or soaked in a solution of table salt, and then silver nitrate was brushed over. A chemical reaction occurred, precipitating light-sensitive silver chloride directly into the fibres of the paper, where it was physically trapped. The ratio was an exquisitely tricky one, a question explored in Dr. Mike Ware's Mechanisms of image deterioration in early photographs: the sensitivity to light of W.H.F. Talbot's halide-fixed images, 1834-1844 (London: National Museum of Science and Industry, 1994).

2. WHFT found that by alterating several applications of salt and silver that the sensitivity of the paper was increased, a crucial step towards its use in the camera.