What is left in a silver gelatin print after standard development

litody · Oct 31, 2012

This is something I have often wondered about. We here about all sorts of so called archival processes that protect, coat and / or convert the silver in a print to something more stable. But if I'm not mistaken silver is, well silver. It isn't black and what the image is made of in my images is black.
Silver Oxide is black. That is the colour that silver tarnishes/oxidises to when exposed to the air, especially silver plate. So all you chemists, what is the black in my silver prints and is there really any elemental silver left in silver gelatin prints at all or is there only some silver compound or salts left after normal processing.

Products like Sistan are just coatings (can easily be washed out), Selenium converts to Silver Selenide but what is it converting to Selenium Selenide. Is it silver oxide being converted or silver under a surface coating of oxide being converted. Just what exactly?

Gerald C Koch · Oct 31, 2012

The image is composed of very fine particles of metyallic silver which appear black or brown as in warmtone papers. The size of the particles determines the color which we see. The developer is a strong reducer so there is no silver oxide in the print.

litody · Oct 31, 2012

so are you saying its the crystaline structure of the silver particles that dictate the color? Can anyone elaborate on this?

Ian C · Oct 31, 2012

“The color of a silver image depends upon the size of the silver grains that go to make it up. An image mainly composed of very large, coarse grains will be blue-black in tone; if the grains are somewhat smaller, the tone will be neutral-black; and if the image is composed of mostly very fine grains, the image will be warm-black or even deep-brown.

The natural color of a silver image is black. There are, however, many occasions when a warmer tone, from a sort of ivory-black through brown-blacks, to deep brown and sepia, is more appropriate for a given subject. If only a small warming up of tone is required, it can be accomplished by proper choice of paper and developer. For more pronounced tones, an after treatment of the finished print is required; this is known as toning."

(Excerpt from out-of-print 1976 Amphoto Home Darkroom Course by John S. Carroll)

ath · Oct 31, 2012

It's all in the interaction of light (electromagnetic wave) with the surface of the metallic particle. This interaction changes significantly if the size of the metal is in the order of the wavelength. Large particles reflect light due to the electrical conduction on the surface; with smaller particles this changes to interference, resonance (these generate the "colour" of the silver in a print) and absorption. The wavelength of green light is ca. 0.5µm.
It's the same reason why thin sheets of metal appear opaque and not reflective.

cliveh · Oct 31, 2012

The colour of developed silver changes with the particle size (see Mie theory of scattering). However, when particles are closely packed together, as in a photographic emulsion, the Mie theory is no longer valid and the colour is very much darker. The tight packing of chemically developed filamentary silver ensures a neutral black. This black colour (yes I know it is not really a colour) appears to be due to multiple scattering and absorption of the light.
Does that help?

nworth · Oct 31, 2012

The combination gets pretty complex and is usually not uniform. There is silver, as described above, and gelatin, and water, and air, with all its components and contaminants. There are also usually some residual processing chemicals, but hopefully not much of any of them. The paper also influences the environment, and it is usually coated with some chemicals. It's the residual chemicals and stuff from the air that diffuse through the gelatine to attack the silver. If you tone the print, the toner partially converts the silver to some colored material. For the common sulfide and selenium toners, that material is silver sulfide and silver selenide, which are more stable than silver metal. For gold toners, metallic gold is plated out onto the silver. Other toners convert the silver to less stable colored materials. Of course, the toners also leave behind some residual materials that mostly get washed out.

litody · Oct 31, 2012

cliveh said:
This black colour (yes I know it is not really a colour) appears to be due to multiple scattering and absorption of the light.
Does that help?

Actually black is a colour. Colour is not a property of a light wave, an electro magnetic wave, a photon or whatever you want to call it. Colour is a human perception derived from the presence or lack of different wave lengths and perceiving black is as valid as perceiving any other colour. And infact you can close your eyes and imagine any colour you like. But I digress.

I just read a little of Mees and it confirms what you've all been saying in varying degrees. Crystal shape and size, development by-products (and oxidised by-products) all contribute to the crystal structures, coatings and how much light and which wavelengths they absorb. And the medium the crystals are contained within (gelatin) etc.

I should have read it sooner I guess.

Thanks

AgX · Oct 31, 2012

"Rays are not coloured"
W.D. Wright

Gerald C Koch · Oct 31, 2012

litody said:
Actually black is a colour.

Technically what we observe as black is merely the absence of light. Objects that appear black reflect very little light. You will not find black on the color wheel. It is neither an additive nor a subtractive color.

Vaughn · Nov 1, 2012

Complicate matters by realizing that tonality we see is not derived from the light reflecting off the surface of the paper -- but from the amount of light blocked by the silver while passing thru the emulsion, the remaining light reflecting off the base and us seeing what light manages to make it through the emulsion again and to our eyes.

What is left in a silver gelatin print after standard development

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