example of a photogram from Britain.co.uk
Toronto. By 1802, the sensitivity of silver halides to light was known in scientific circles. Thomas Wedgwood managed to make ‘photograms‘ – silhouettes on leather but could not make the photograms permanent. The delicate images – even kept in darkness – slowly turned completely black.
The first successful photographic processes by camera were announced in January, 1839 after it was discovered that a mild salt solution could ‘fix’ images and prevent them from turning black over time.
In 1840 Hippolyte Bayard, suggested that a solution of hyposulfite could act as a better fixer bath. The term ‘hypo’ remains in the lexicon today as a name for the fixer bath in film photography (even though the actual chemical turned out not to be hyposulfite).
Basically, the developer solution turns light exposed silver halides (clear) to metallic silver (black). The fixer solution is CRITICAL. It removes all the remaining silver halides so they cannot turn to black metallic silver. A good wash removes the now released halides and other chemicals from the film or paper.
Note. The title of this post is a riff on the name of Oscar Wilde’s play, “The Importance of Being Earnest“.
