The Life, Death & Possible Afterlife of POP
Many photographic materials have been discontinued in recent years. Usually it is because their usage has fallen to the point where they are no longer economic to produce, sometimes because their manufacture raises health and safety issues. Unfortunately printing-out paper, or POP as it was always abbreviated, fell into both these categories. It’s a little sad that it went, as it had been available for well over a century, and ceased only when Kentmere, the last manufacturer of the material, was acquired by Harman Ltd in 2007.
Until the 1880’s photographs were printed almost exclusively on albumen paper, which was factory coated with egg albumen, but sensitised by the user prior to printing with a silver nitrate bath. As the paper was relatively ‘slow’ it was exposed by direct contact to same size negatives, the image formed by direct exposure to light, and the final print just needed rinsing to clear excess silver nitrate, and then preferably gold toning followed by fixing. The colour was initially a rich plum tone, which after processing became a refined purple, more akin to modern selenium toned prints.
The first published formula for a printing-out silver chloride paper using gelatin binder was published by Capt. Sir William de W. Abney in 1882, and was the logical successor to albumen paper, requiring daylight exposure to produce a burnt sienna-tinted image. The emulsion was mixed containing an excess of silver nitrate, which acted as a reservoir of silver, reinforcing the printed-out image. As with albumen paper, its process normally involved washing to remove excess silver nitrate, followed by gold toning, or gold and platinum, to produce a stable purplish image. Liesegang of Dusseldorf were the first company to take it to market in 1886, with the name ‘Aristotypie’.
As soon as the gelatin emulsion process was devised faster papers became available, but were before their time as enlarging wasn’t required yet. Portrait studios worked with large glass plates exclusively, and the working methods of a generation of albumen printers were resistant to change. Consequently, in the 1880’s two new materials became available which negated the need for sensitisation by the user; collodion printing-out papers and gelatin printing out papers. These used proper emulsions, but bridged over from the albumen days to yield a similar result, by containing an excess of silver nitrate, which strengthened the density, colour, and tonal range.
A POP paper researched by Joseph Barker of London was offered for sale in 1885 but failed to make any impact, before being taken up by Emil Obernetier in Germany. Eventually, in 1891 the Britannia Works, soon to be Ilford Limited, manufactured Barker’s paper, and coined the marketing abbreviation POP which has stuck ever since. Eastman Kodak knew a good thing when they saw it, and quickly came in with ‘Solio’ paper in 1892.
Self-toning versions of POP, containing gold salts, were available by the early years of the 20th century, and became the most popular in use. By the mid 1890’s there were many manufacturers of POP, and simply from the weight of advertising material devoted to the materials, clearly POP outsold developing-out paper by two-fold. Sales records from the USA show POP supplying 60% of the market in 1899.
Eastman Kodak introduced it’s first ‘Solio’ POP in 1892, and virtually all manufacturers of photo printing papers in Europe & Northern America followed them. Through the 20’th century a long slow demise followed, with Kodak deleting it’s last POP ‘Studio Proof’ in 1987. However the French company Guiliminot took it on themselves to continue, and after their demise in 1995 Kentmere Ltd took over production.
An unusual industrial application kept POP in production at Kentmere. During the cold war a means of recording the locations of atomic bomb strikes across the UK was required, so that regional planners could react quickly to the strikes. A system of recording sensors was maintained across the UK, and the sensitive material used in them was a resin coated version of POP. The war game never happened, of course, but the paper was a nice little earner for Kentmere for a long time. After 1990 this market soon vanished, but Kentmere took another formula from The Chicago Albumen Company, and custom-made it for this distributor for many years. It all came to an end when Harman acquired Kentmere in 2006. Several last runs of POP were made before the Kentmere plant finally closed, some of which makings failed, which had been a regular ocurrence anyway.
Harman found their Mobberly plant was unsuitable for POP production. Rephrasing that, there was no way Harman were going to put a filthy silver nitrate saturated product like POP down their coating alley. The excess of silver nitrate that must be present in the emulsion is death to all normal emulsions & the clean-up costs on the coating system would make it prohibitive to produce.
But the other big problem with traditional POP is that the emulsion had to be mixed quickly and coated at a higher than normal temperature, during which time it was still digesting, and meanwhile the characteristic were changing. One end of a roll may have rather different properties from the other, and some of it may be so out of specification that it might have to be scrapped, which was a constant overhead on Kentmere’s production. Kodak had a stabilised version worked out with ‘Studio Proof’, but 30 years on after it went there’s no sign of their formulation surfacing. So in 2006 an elderly Victorian piece of photographic technology was laid to rest, some mourners but not enough to matter.
The end of the story? As a manufactured product possibly, none of the few remaining photographic coating operations show any interest. But as as a home-made option there may be life there yet. Foma, the photo paper manufacturer from the Czech Republic recently introduced a new slow ‘gaslight’ speed chloride paper. An experiment was made the experiment to see how it reacted to a silver treatment, placing an excess of silver nitrate into the emulsion to mimic the composition of a POP. The actual treatment was a 1% silver nitrate solution, made with 10g silver nitrate into 1 litre of deionised water, with the addition of 5 grams of potassium citrate. The FB double weight ‘Fomalux’ was treated in the solution for 10 minutes, then drained and allowed to dry on blotters, before being trimmed and used for contact printing to daylight with a test negative.
The quick test was interesting & calls for more investigation. Untreated paper yields thin pale blue/violet results, with poor maximum density, interesting but limited. The silver nitrate treated paper was significantly faster, while delivering more density, improved tonal range, and a colour dating back a century. So if the workers in the 1870’s had to apply a sensitising bath to use their paper, should we really assume POP is dead, when possibly all we have to do is apply the same principal?