Photo students –
We will be stinking up the joint by sepia (more specifically, sodium sulfide) toning prints on Wednesday, Nov 30 at 9AM. Be sure to bring UNMOUNTED prints – you’ll even have time to make a b/w print, wash it, and tone it.
Sepia toning is a specialized treatment to give a black-and-white photographic print a warmer tone and to enhance its archival qualities. Chemicals are used to convert the metallic silver in the print to a sulfide compound, which is much more resistant to the effects of environmental pollutants such as atmospheric sulfur compounds. Silver sulfide is at least 50% more stable than silver.
There are three types of sepia toner in modern use;
- Sodium sulfide toners – the traditional ‘rotten egg’ toner;
- Thiourea (or ‘thiocarbamide’) toners – these are odorless and the tone can be varied according to the chemical mixture;
- Polysulfide or ‘direct’ toners – these do not require a bleaching stage.
Except for polysulfide toners, sepia toning is done in three stages. First the print is soaked in a potassium ferricyanide bleach to re-convert the metallic silver to silver halide. The print is washed to remove excess potassium ferricyanide then immersed into a bath of toner, which converts the silver halides to silver sulfide.
Incomplete bleaching creates a multi-toned image with sepia highlights and gray mid-tones and shadows. This is called split toning. The untoned silver in the print can be treated with a different toner, such as gold or selenium.