The Fog of Printing
January 4, 2013
High-quality, affordable inkjet printers made it possible for the first time for photographers to make beautiful, long-lasting color prints in their home or studio without the hassle and expense of setting up a wet darkroom. There is a pitfall in paradise, however, which can trip up unwary photographers who like to print their work. In the trade, the problem is called outgassing.
Like many photographers, I learned about this problem the hard way, when a client called me to complain about a peculiar fog that had developed on the inside of the glazing (the picture glass) that I had used on his matted-and-framed print. A little research revealed the source of the fog. All inkjet inks contain glycols, oily substances that help prevent nozzle clogs by causing the ink to dry more slowly. Slow drying is good when the ink is inside that expensive print head, but bad once the ink hits your paper. If you frame an inkjet print before the glycols have dried completely, they will continue to evaporate off the surface of the print and condense on the inside of the glazing. The problem is most pronounced near the darkest shadows because they have the greatest ink density. Unfortunately, there's no clear visual indication when the glycols have evaporated completely. You can only adopt a drying procedure that testing has shown will prevent outgassing.
Fortunately, outgassing doesn't ruin either the glazing or the print. However, it does require you to disassemble the framed print, clean the glass, allow the print to finish drying, then reassemble the framed print ‒ an enormous hassle, particularly for large prints.
Resin-coated papers, also called RC or barrier-style papers, are more prone to this problem than "fine art" papers. RC papers contain an impermeable layer that prevents the ink from penetrating deeply into the paper. That helps produce brighter, glossier prints, according to Epson, but also increases the risk of outgassing. Fine-art papers lack this barrier layer. Residual gases can be absorbed into the paper, where they are is less likely to evaporate. According to my testing, however, claims that fine-art papers are completely immune to the problem are simply wrong.
Preventing the problem is obviously much better than placating unhappy clients and reframing prints. Epson claims that putting a sheet of plain paper in contact with the print for 24 hours should usually absorb all the glycols. If the plain paper is wavy after 24 hours, Epson goes on to say, change the paper, give the print another 24 hours, and it will be ready to frame. In my experience, however, this method of drying is unreliable. Here's my solution. As soon as possible after printing, I mount the print on foam core and place it uncovered in a south-facing window. There it sits for three days, more if the days are cloudy. The sun will warm the print perceptibly, which significantly accelerates the drying process. I've taken prints dried with this procedure, framed them, then baked the framed prints in direct sun for two days and found no outgassing. If I'm in a big hurry, I borrow my wife's hair dryer and blast the print with hot air for five to fifteen minutes. The exact time depends on the size of the print. The key here is gentle heat. Drying at room temperature takes far longer than drying in the sun.
My testing has shown that putting a print made with Epson Ultrachrome K3 inks in the sun for three days won't fade it. In fact, I placed a test print in the sun over six months ago, and there's still no visible fading compared to a print kept in fluorescent room light, out of direct sun.
I certainly haven't tested every possible combination of paper and ink on the market, nor do all of my readers live in Boulder, Colorado, with its abundant sunshine. You should do your own testing with your printer and your favorite paper to determine a procedure that reliably prevents outgassing.