Henry William Jackson glass negative from NGM 1989/2 , Is it colorful ?

[Mark Sawyer]

There are several possible reasons. My amateur suggestion; It may be that the emulsion is "mirroring" due to deterioration, from improper processing and/or storage...

Not sure, but I think the mirroring Mark is referring to is silver migration, where the metallic silver migrates to the surface and forms a reflective metallic sheen that may have various colors common to tarnished silver. I don't think it's that though, as that shows up in reflected light, and in this case, the negative is backlit. The reddish brown area in the denser tones may be silver sulfiding, where sulfur from residual fixer (sodium thiosulfate) combines with the image silver to form silver sulfide, which has brownish hues. (That's why we wash our film and prints so thoroughly.) I'll be interested in what Mark's conservator wife thinks.

It could also be that the photo of the negative simply had the color saturation slid up too high.

[Mustafa Umut Sarac]

dichroic or dichroism: "Glass or crystals showing different colors when viewed from different directions, or having different absorption coefficients for light polarized in different directions" Many years ago used this extensively in Photomicrography of prepared specimen slides.

Greg , can we say that silver or silver iodide crystals caused these colors , if they are in really crystal form ?

[Mustafa Umut Sarac]

Not sure, but I think the mirroring Mark is referring to is silver migration, where the metallic silver migrates to the surface and forms a reflective metallic sheen that may have various colors common to tarnished silver. I don't think it's that though, as that shows up in reflected light, and in this case, the negative is backlit. The reddish brown area in the denser tones may be silver sulfiding, where sulfur from residual fixer (sodium thiosulfate) combines with the image silver to form silver sulfide, which has brownish hues. (That's why we wash our film and prints so thoroughly.) I'll be interested in what Mark's conservator wife thinks.

It could also be that the photo of the negative simply had the color saturation slid up too high.

Mark , really interesting , lets wait what she says ?

[John Layton]

If the pinkish color were only present in the shadows then I'd say it was something like crocein scarlet, which would be applied to help retain shadow details in prints. But this does not look so deliberately applied - so either chemical and/or age-related artifacts (such as the sulfiding as described above) or something in the way the backlight affected the photo of the negative.

[Greg]

Greg , can we say that silver or silver iodide crystals caused these colors , if they are in really crystal form ?

I think so. I was photographing specimens from about X2 up to X100 magnification. I think the solidified medium that they were in acted more like glass, but maybe the solidified medium had a microscopic crystal structure to it... Never was able to determine exactly what caused the dichroic colors.

[Mustafa Umut Sarac]

I remembered my research on colorants and different crystal shapes of silver in glass was creating wide range of colors , pyramid shaped crystals were creating one color and the sphere and so on. And colors were appearing with backlighting. I had been read that effect was invented by romans more than 2000 years ago and one of the glass vase was creating enourmous color changes with different temperatures of light. french cathedral near to paris was named as blood of jesus and glass panes was creating blood color with the setting sun and tones were fluiding from top to bottom. I learned this glass was used at middle ages at cathedrals widely. I had been found a picture with these crystals in liquids and backlighted and they were creating attached wetplate colors , extremelly similar. I forgot the name of that technology but I think it is still produced by a factory which served to tiffany .

[Jim Jones]

I believe profvandegraf in post #5 has the most likely answer: blue window lighting and incandescent artificial lighting causing an illusion of color in the glass plate.

[thegreatcornholio]

From my experience you get very cold colored negatives (blue/black) when you either develop very long or intensify/redevelop your negatives. It comes from the reduction of iodides to metallic silver thus a very dense negative (what you would target for POP papers).

It's very interesting to see original negatives, are there more images of Jackson's negatives around?

[John Layton]

William Henry...not Henry William! (c'mon guys...jeeesh!)