Fixing is the process of removing from photographic materials the unused light-sensitive solutions, thus making the image more permanent.
Had Thomas Wedgwood been able to fix his pictures, the invention of photography would have been attributable to him. However, it was not until after his death that Sir John Herschel discovered what Wedgwood had found so elusive. In a paper printed in the Edinburgh Philosophical Journal ( 8 January 1819) Herschel wrote "Muriate of silver (now known as silver chloride), newly precipitated, dissolves in this salt (hyposulphite)....almost as readily as sugar in water."
Sodium thiosulphate (incorrectly known as Hypo) is still, in fact, a fixing agent used today.
Though fixing made prints more stable, fading was at first a problem that needed to be addressed. One of the causes was inadequate washing of prints after processing. It was this instability that caused people to investigate more lasting processes such as the Carbon one.
© Robert Leggat, 1999.