Acidifying and De-acidifying paper for platinum printing
March 5, 2012
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 deacidfication, 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 deacidification, as the name suggests, involves the removing the acid from a particular paper. My initial thoughts were that Penn was removing the acid before he was coating the paper, which goes against the normal practice for ‘acid free’ type papers like BFK. Having discussed this with other printers, it is more than likely that the Penn note signified the print had been de-acidified after successive coatings/developments, using calcium or magnesium bicarbonate (The Barrows method). I would imagine after three successive coatings and exposure cycles the print would have been in a heavily acidic state and would require quite lengthy deacification. I know from my own research that multi-layered platinum/palladium prints can take significantly more time to clear completely when compared to those of a single layer.