But that defeats the whole purpose of POP, adding a development stage...
Actually, no. The great attraction of POP is that it is self-masking (the emulsion under the thinnest portions of the negative darkens early in the exposure, which absorbs light and prevents the shadows from going black while the highlights print in. For permanence, POP has to be wet-processed, and development is not all that different from the usual gold toning stage.
In any event, we are talking about enhancing and preserving images on non-POP stock, another game entirely. It is indeed unfortunate that Ilford decided not to maintain the Kentmere POP production; the stuff really is unique.
(Incidentally, there is at least one bizarre process for self-masking which involves exposing regular paper after wetting it with developer, in order to compress the tonal range so that the resulting print can be used as a paper negative. I've tried it, and it is a mess, as well as being very finicky.)
So what makes a POP paper so difficult to produce?
I understand that if the ratio of silver nitrate and sodium chloride is swapped, you get the other kind of paper. Meaning, and I'm not sure which being greater creates what, but more of one and you get a POP and more of the other and you get a DOP. Couldn't the emulsion tinkerers just as easily create a POP? Or is there more to it?
Probably nothing. But a related question might be what makes POP paper so difficult to produce economically? Most likely the answer is sales volume.
Originally Posted by holmburgers
Well, there's some older thread around here that talks about high temperatures, worker's safety and so on; i.e. Ilford's decision to not continue production. So there's something else; but no doubt it all goes back to sales volume.
What I mean is, why don't WE make one?!
A quick search failed to turn up the relevant thread, so from memory the story is: Ilford discontinued some of the Kentmere papers (specifically, Kentona) because of the requirement for cadmium in the formula; this was attributed to worker safety issues but is more likely to have been driven by environmental regulatory considerations. Kentmere POP (marketed by Chicago Albumen Works) would not be placed into production on the Ilford machinery because the working temperature range of the existing equipment did not extend high enough for the POP recipe. Modification of the equipment for such a marginal product was not regarded as economic. Presumably development of an alternative POP formula would also be uneconomic.
With any luck, someday one of the smaller European manufacturers will create a marketable POP; if Azo can be recreated and sold at a profit, presumably there is also a chance (however small) for POP---especially if an exact match to an existing product is not needed.
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That's exactly the story I remember from the post.
Now, w/o fear of straying from the original topic, I'm curious about Azo paper. What can you tell me about it? Is this the fabled "contact" paper? That's what I'm gathering from "azo paper"->Google->MichaelandPaula.com. Or, perhaps I'm thinking about silver-chloride paper, which it appears they also have.
holmburgers: since you started the thread, I think that you have the hereditary right and privelege of initiating a digresssion
Azo was the last of the traditional chloride contact-speed papers, although I think that in addition to the Michael and Paula Smith product, there is at least one Eastern European chloride paper on the market now. These papers are contact papers only because pure chloride emulsions are inherently not very sensitive; they can be projection printed but only if the light is rather intense.
The appeal of chloride emulsions (apart from romantic notions and the desire to identify with the greats of the past who used it) is in the long tonal scale and excellent blacks, especially with amidol developers. The traditional versions also tone well, although I don't know if this is chemical (a simple emulsion without all the silver-economizing and curve-adjusting tweaks) or mechanical (Azo originated far enough back that overcoating hadn't been invented; I don't know if it was incorporated later or not).
The Smiths had built their business around ULF contact prints, and preserved the availability of Azo for a time by contracting to buy the entire annual production (or close to it, anyway) so when Kodak finally pulled the plug, they undertook to get a replacement into production (the history of this is extensively documented on the Web, and will undoubtedly be the basis of business-school case studies someday).
Azo really is wonderful stuff (like many others, I am hoarding the last of my supply against really special uses) but I can't speak to the currently-available replacements.
(There is also a certain cachet associated with the use of a paper that can only be contact printed, especially if you are using a negative bigger than 8x10 )
AFAIK, since it's a chloride emulsion, it has fine grain and so it is "toner friendly". Bromide papers are coarser grained and don't tone that drastically. Chlorobromide emulsions vary, according to the chloride content.
Originally Posted by greybeard
Take that posted example and do the following:
Under a red or yellow safelight...
Bleach in very weak Dichromate/Sulfuric Acid bleach unil the negative image vanishes.
Treat with dilute Sodium Sulfite
Under normal room lights....
Develop in Dektol 1:3 until you are happy with the image
You should have a good positive image, but reversed left to right.
Oh, and Azo paper will be reasonably high in speed to daylight as it is very UV sensitive unless you are using a modern lens with good UV coating or have a UV filter you are using. It will give a different colored image than the Kodabromide as one is a Chloride paper and the other is a Bromide paper (guess which is which )
do you have any magic potions that will fix the negative image without processing it to be a positive print ?
i have a series of negative that i have fixed in spent speed fix, and while the image faded and sort of vanished
the paper stayed white. i also fixed some in a weak hypo solution
and the images faded ( not as bad as the speed fix )
but the paper kind of stayed a darkish tone ... and/or got darker
i'd rather not use dichromate+bleach + and later dektol to make a reversal process ...
part of the fun of this faux pop process is that no developer or crazy chemistry is needed.
while i don't mind this process being the first step to something hybrid, i would love it
if the images could be fixed and a bit more permanent on the paper,
they even get darker whenever i look at them in low light