I really don't understand why this is important to some people. Salt is not a practical fixing agent. Talbot's early salt prints faded quite rapidly. A few survived and are in a British museum where hey can be viewed only for a brief period under very dim light. They are not fixed in any sense of the word. Fortunately Talbot switched to hypo.
However, this is very interesting (well, I mean of course, it is interesting to me), because it seems to indicate that while many authors (and "authorities", viz Dr.Mike Ware) refer to Talbot "stabilising" his early prints in salt solutions, that he was actually fixing them, but fixing them incompletely. A photochemist would not call what has been done "stabilising" except perhaps as a loose or conversational term.
Hi, Alan:http://resources.conservation-us.org/pmgtopics/1993-volume-five/05_10_Reinhold.pdf
Here is a description of Fox Talbot's early process (though any negative could be contact printed on such paper).
Since the stabilized print is darkened by light I tried to fix one instead, by immersion in near saturated salt solution at room temperature for 24 hrs.
The brown-purple pic is of the paper after exposure to sunlight for 3 min and washing ; the yellow pic shows the same after fixing in salt solution for 24 hrs.
A sample of the yellow print was placed in Rodinal !:50 for 20 min with some agitation, it did not darken, confirming that the yellow print was fixed.
So fixing of prints in salt solution is possible but who would want a yellow print. View attachment 180823 View attachment 180824
My sense is that the color change is related to physical removal of the silver chloride resulting in smaller effective grain size responsible for light scattering - yellow being shorter than the red wavelength. Therefore, it would seem that unfortunately one can not remove the chloride (complete fixing) without the color change.
I don't pretend to completely understand this. You are suggesting that somehow the silver chloride contributes to a larger grain size, for example, some AgCl could be involved in "holding together" the larger grains. If that is true, and it fits everything I've seen, then it does mean that it is physically impossible to fix the print without changing the color.
And in some ways the situation is even worse than you have suggested ( from the standpoint of trying to preserve the color ): if it was just that simple, it might be possible to heavily overprint and then recover the original color in the fix. But that doesn't work, and a heavily overprinted salt print will still turn brown in salt water and in hypo. So even if we overprint to the point of bronzing, when the AgCl is removed it divides even the biggest grains into small ones, just more of them! i.e. the AgCL is throughout the grain structure. Making bigger grains during printing cannot help.
I don't know if this is all true, but it sure fits the facts of experience very well. Honestly it's a little disappointing... I was still holding out some hope that the original color might be preserved somehow. Clive's approach of photographing the original with color film might be the closest we can get to "preserving" the look, short of storing an unfixed and unstabilized print in a dark drawer.
Gerald, as a chemist, do you not have any curiosity as to the history of your profession?
Is it not interesting to you understand what the processes were that were occurring when the alchemists of the 14th century were experimenting with their peculiar mixtures, and yet achieving something similar to what happens in today's laboratories?
You are after all, someone who frequently admonishes others to do their research before asking a question, and here we are undertaking collaborative research into the history of a photographic chemical process, and yet you admonish us for doing so!
Sometimes, it seems hard to "win" ... or, to put it another way, damned if you do, damned if you don't
One must distinguish between chemistry and alchemy.
Please it is simple to test for residual silver and find that soaking a film or print for any reasonable time in a salt solution does not remove enough silver from a the film or print to claim that it is fixed.
I know that some are always seeking a cheaper alternative but hypo is cheaper than film or paper.
OK Gerald I give up. I have the greatest respect for you and have learned much by reading your posts, but in this case you seem to be being deliberately obtuse. It really is rather disappointing.
I can recall that when I was making lots of photogenic drawings, I had a large supply of AgNo3 (about £1 a gram at the time) and was therefore able to make many experiments. My note keeping was non-existent, so I am not able to quote concentrations. However, I did conduct a series of tests where I varied both the silver nitrate concentration and salt concentration for the original sensitisation. Still stabilising with a saturated salt solution, I once produced an image with little colour, but was light fast in direct sunlight for many hours, and noticed no fading as though fixed. My conclusion is that with a certain combination of AGNo3 coupled with a certain concentration of salt will yield a very stable image. But this is just conjecture on my part and don’t experiment with those chemicals much these days.
During fixation the prints undergo a dramatic change in color, in which the original brilliant purple or brown color is transformed into a much yellower and duller brown hue, accompanied at the same time by a loss of density. The reasons for this color and density change--a characteristic phenomenon in all silver printing-out papers--have to do with the physical structure of the metallic silver which forms the image.
{my emphasis}As soon as the print hits the hypo, contrast and density increase again.
It's sort of amazing how complicated such a "simple" process is!
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