than silver. There are three types of sepia toner in modern use; Sodium sulfide toners – the traditional 'rotten egg' toners (sodium sulfide smells of rotten eggs when exposed to moisture); 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. The print is first soaked in a potassium ferricyanide bleach to reconvert the metallic silver to silver halide. The print is washed to remove excess potassium ferricyanide and 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. Fred Judge FRPS made extensive use of sepia toning for postcards produced by the British picture postcards manufacturer Judges Postcards. Metal replacement toning Metal replacement toners replace the metallic silver, through a series of chemical reactions, with a ferrocyanide salt of a transition metal. Some metals, such as platinum or gold, can protect the image. Others, such as iron (blue toner) or copper (red toner), may reduce the life of the image. Metal-replacement toning with gold alone results in a blue-black tone. It is often combined with a sepia toner to produce a more attractive orange-red tone. The archival Gold Protective Solution (GP-1) formula uses a 1% gold chloride stock solution with sodium or potassium thiocyanate. It is sometimes used to split tone photographs previously toned in selenium for artistic purposes. Dye toning Dye toners replace the metallic silver with a dye. The image will have a reduced lifetime compared with an ordinary silver print. Digital toning Toning can be simulated digitally, either in-camera or in post-processing. The in-camera effect, as well as beginner tutorials given for software like Photoshop or GIMP, use a simple tint. More sophisticated software tends to implement sepia tones using the duotone feature. Simpler photo-editing software usually has an option to sepia-tone an image in one step. Examples The examples below show a digital color photograph, a black-and-white version and a sepia-toned version. The following are examples of the three types using film: See also Color grading Cyanotype Film tinting Grisaille (painting)