"This is a problem that is specific to a type of paper, mainly "RC" or
barrier type photo inkjet papers. The problem is not specific to Epson brand
"RC" papers --there are many other brands that share these specifications.
The problem is not even limited to our industry.
The out-gassing fog comes from the glycol, a wetting agent that is used in
all inkjet inks. "RC" photo inkjet papers have a barrier layer (usually
polyethylene) between the inkjet receptive coating and the paper base. This
barrier prevents heavy ink loads from wicking into the paper (lowering image
resolution, contrast and color saturation) and from moisture that causes
paper "cockling" (deforming wrinkles). However, this same barrier can
prevent the ink from drying quickly. Although the paper may appear to be dry
(and is dry to the touch, especially "fast-drying" micro-porous papers like
Epson's "Premium" line), there is still plenty of water and glycol under
that super-absorbent coating, lying against the barrier layer.
It is this water and glycol, trapped against the barrier layer, that may
eventually out-gas (evaporate) and condensate (fog) on the inside of the
glass, if a print is framed before it has had a chance to sufficiently dry.
Some have noticed that the fog on the glass is "oily" to the touch. This is
from the glycol.
People in the inkjet signage industry have long ago noticed that they must
let their RC type photo papers dry for several days before they can thermal
laminate these papers -- otherwise the trapped water and glycol will
immediately turn to steam and create bubbles between the laminate and the
paper. Some RC papers never dry quick enough (who can wait two weeks?) to laminate.
A spokesman from a third-party inkjet ink company recently told me that it
was once necessary for them to change their glycol ratio in the inks used in
HP printers, otherwise their inks never did seem to dry a host of media types.
Epson's new pigmented UltraChrome inks (and any of their other inksets) have no glycol drying issues on matte and fine art papers. There are also no
drying problems (that we know of) with their cast coated glossy photo
papers, i.e. the Epson Photo Paper (now called "Glossy Photo Paper") and
their Glossy Paper Photo Weight (also called "Professional Glossy Paper" in
the sheet size).
Accelerated drying procedures may be needed when framing Epson "Premium" papers (and all other RC type papers) behind glass to avoid out-gassing fog on the glass. Epson and other companies suggest waiting at least two weeks before framing barrier type photo inkjet papers behind glass. Epson's Greg McCoy has another suggestion for those needing a quicker solution:
"The process needs to be accelerated, and by 'curing' the print with a plain
piece of paper in contact with the print for 24 hours.
"After 24 hrs, you will notice the plain sheet of paper is wavy.
"On a print with heavy ink duty, I recommend changing the paper after 24 hrs and a new sheet and let it sit another 24 hrs.
"This is necessary for any print on a barrier paper that will be framed
under glass or placed in a plastic sleeve.""