The Green Hues of an Iodide-based Gelatin Silver Print

The deep green hue of this gelatin silver print is unusual and is outside the range of what is generally possible by selection of papers and developers, so we used XRF analysis to dig a little deeper. Other than the usual gelatin silver prints suspects (silver, barium, and strontium) the only other peak is a very small peak at about 7.48KeV, just right for the K-alpha peak of Nickel. At first we thought we had discovered a new nickel-based toner, but soon realized that the nickel peak is due to internal components of the portable XRF unit, so it appears that while unusual the green is not the result of toning but rather an unusual paper. After a little research we found this article on green-hued prints: http://unblinkingeye.com/Articles/Green/green.html. It seems that silver-iodide based gelatin silver prints sometimes show this green tonality. The early 20th century subject matter fits with the iodide papers available at that time.

Mercury-Intensified Cellulose Nitrate Negative

Although exceedingly poisonous, mercury salts were used in various formulations by photographers for the intensification of negatives in the 19th century and well into the 20th century. If a negative was underexposed and needed more density in order to make a good print, intensification was one of the best alternatives. Mercury intensification also generally led to fading of the negative over time. This faded 4"x5" cellulose nitrate negative had the faded and slightly yellow quality of an intensified negative (though sometimes they are a more brilliant yellow color), so we confirmed our suspicions with XRF analysis. The presence of mercury (Hg) is confirmed by mercury's L-alpha peak at 9.99KeV. More on this after further analysis.

The Iron-Toned Blues

The iron-based toners for use on gelatin silver prints bear a striking similarity to the chemistry of cyanotypes, which explains the nearly identical range of blues found in iron-toned gelatin silver prints and cyanotypes. The blue of the cyanotype was an often derided color, so it's not surprising that the blue toners were seldom used. Other than this 5" x 7" found at a flea market, the only iron-toned gelatin silver prints we are familiar with are those made by Edward Curtis during his Hollywood years in the 1920s, typically film stills or Aphrodite imagery.