The Broad Tonal Range of Platinum Prints

Spectrum 1

Platinum prints are neutral black with some brown present in the mid-tones.  The sensitizer for platinum prints  consists of ferric oxalate and platinum salts.  Upon exposure to light, the ferric oxalate reduces to ferrous oxalate.  When the paper is submerged in the developer, ferrous oxalate reacts with the platinum salts.  The platinum salts reduce to metallic platinum and form the resulting image.  

Compared to other photographic processes, platinum is more resistant to deterioration because it is chemically less active.  The greatest concern facing platinum prints is the deterioration of the paper support (often a result of insufficient clearing or washing). Residual iron (Fe) degrade the cellulose in paper fibers and can lead to yellowing, foxing, decreased contrast, and increased fragility.  In Spectrum 1, the platinum (Pt) peaks decrease significantly from the areas of maximum (blue) to minimum (red) density.  Small peaks of nickel (Ni) and zinc (Zn) are also present.

In the spectra below, a gradual decrease of the platinum peaks can be observed.  Spectrum 2 compares maximum (red) to middle (blue) density.  Spectrum 3 compares middle (red) density to minimum (blue) density.

Spectrum 2

Spectrum 3