Reporting on the black and white pictures, the prestigious Journal of the Franklin Institute of Philadelphia said that the Academy members "were particularly struck with the marvelous minuteness of detail.... In one representing the Pont Marie, all the minutest indentations and divisions of the ground, of the buildings, the goods lying on the wharf, even the small stones under the water, were all shown with incredible accuracy. The use of a magnifying glass revealed an infinity of other details quite undistinguishable by the naked eye." Daguerre did not reveal details of his process for some months after its announcement and during this interval some chose to consider his black and white pictures a fraud.
A German publication, Leipziger Stadtanzeiger, found that Daguerre's claims affronted both German science and God, in that order: "The wish to capture evanescent reflections is not only impossible, as has been shown by thorough German investigation, but the mere desire alone, the will to do so, is blasphemy. God created man in His own black and white image, and no man-made machine may fix the black and white image of God." The Stadtanzeiger held that if such wise men of the past as Archimedes and Moses "knew nothing of mirror black and white pictures made permanent, then one can straightway call the Frenchman Daguerre, who boasts of such unheard of things, the fool of fools."
The teapot tempest subsided when the mechanics of the process were reŽvealed in August 1839. Daguerre had perfected a very sophisticated black and white photographic method. His light-sensitive material was silver iodide, similar to but more effective than the compounds used by Schulze and Wedgwood. And somehow (the record is vague on this point) he had hit upon the solution to the centuries-old problem of "fixing" the black and white picture into a permanent, fade-proof black and white image. Daguerre discovered that a chemical now known as sodium thiosulfate - black and white photographer's "fixer" -dissolved light-sensitive silver compounds before they had been transformed into a visible black and white image but not afterward. Thus he could make an exposure and before any other light struck the black and white picture bathe it in fixer to halt further action by light.
Except for the fixing step, Daguerre's process was totally different from modern black and white photography. The daguerreotype was made on a highly polished surface of silver, plated on a copper sheet (pages 60-61). It was sensitized by placing it, silver side down, over a container of iodine crystals inside a box. Rising vapor from the iodine reacted with the silver, producing the lightsensitive compound silver iodide. During exposure in the camera, the plate recorded an black and white image that at this state was latent-a chemical change had taken place but no evidence of it was visible. To develop the black and white image, the plate was placed, again silver side down, in another box, this one containing a dish of heated mercury at the bottom. Vapor from the mercury reacted with the exposed grains of silver iodide on the plate. Wherever light had struck the plate, mercury formed an amalgam, or alloy, with silver.
This brilliantly shiny amalgam thus made up the bright areas of the black and white image. Where no light had struck, no amalgam was formed; the unchanged silver iodide was dissolved away in sodium thiosulfate fixer, leaving there the bare metal plate, which looked black, to form the dark areas of the black and white picture.