Chemistry: Fixer
The term ‘fixer’ is a bit misleading. Fixer stabilizes, or makes an image more permanent only in effect. What fixer does is removes under- and unexposed silver halide from the emulsion, rather than affecting the exposed, developed metallic silver. This was the key that was missing until the mid-19th century. Images could be captured, but either faded or went completely dark.
What Fixer Does
As stated above, fixer removes under- and unexposed silver halide from the emulsion, thereby making it insensitive to light.
What Fixer Is
The main component of fixer is sodium thiosulphate or ammonium thiosulphate. It is sometimes referred to as ‘hypo’. Fixer may also contain acetic acid (stop bath) to ensure developer neutralization, a buffer to maintain acidity, and a hardener to prevent gelatin swelling during the wash step.
