A common practice by contemporary platinum printers is to acidify certain watercolour/printmaking papers to prevent an acid-base reaction commonly observed when an acid ferric oxalate solution reacts with an alkaline paper surface. The process of acidification is simple and involves soaking the paper in either citric acid or oxalic acid for a certain period of time ranging from 1-15 mins. Usually this not only makes a paper useable for platinum/palladium printing but can lead to a dmax increase of up to .20. Each batch of paper can vary so its important to take regular tests to insure consistent results. Many papers I edition with require acidification and it has become a regular part of my workflow. The process can remove the internal sizing of certain papers and may require the use of a hot press to flatten after the print has dried.
Recently I came across some notes written on the back of a Penn Platinum print that mentioned the process of deacification, which I had not encounted before. The print entitled ‘Sitting Nude Rear’ shown below was printed in June 1994 on BFK Rives and went through 3 platinum/palladium coatings and exposure cycles. The full details are shown below the print
“SITTING NUDE REAR / (NEW YORK, 1993) [in a box]”; stamped and inscribed verso: “HAND COATED BY / THE PHOTOGRAPHER / IP:”; stamped verso: “Deacidified”; inscribed verso: “RIVES PAPER ON ALUMINUM / MULTIPLE COATING AND PRINTING / 1 [in a circle] PLATINUM-PALLADIUM / 2 [in a circle] PLATINUM-PALLADIUM / 3 [in a circle] PLATINUM-PALLADIUM”; inscribed verso: “3/6”; stamped verso: “PHOTOGRAPH BY IRVING PENN / “Print made June 1994”; stamped and inscribed verso:
The process of deacification, as the name suggests, would involve removing the acid from a particular paper, this is the opposite of what contemporary platinum/palladium printers are doing today, as previously mentioned. It would be interesting to learn more about this from other printers. I would have thought BFK Rives in 1994 would have been acid free, but it would seem that this is not the case in this instance.
UPDATE : It is more than likely than the Penn note signified that the print had been de-acidified after successive coatings/developments, possibly using one of the modern chelating agents such di-sodium and tetrasodium EDTA, as opposed to de-acidifying the paper before the initial coating, which would be unusual as acidification is the normal practice for 'acid free' type papers.