Glossy paper pH & dmax
2003-12-26 by Paul Roark
I used my Abby acid test pen on some Epson glossy papers and got some interesting results. Premium Semigloss appears to have an acidic coating with neutral or alkaline paper on the inside. (The color is just slightly purple.) The Premium Semimatte coating at first appears to be neutral, but the pen mark slowly turns yellow, indicating acid. The interior paper is neutral or alkaline. Epson Glossy Photo Paper has an alkaline coating but an acidic paper interior. The initial dmax readings of these three papers appear to be higher the more acidic the coating is. However, after a week or so, the dmax readings seem to get closer together. The sprayed and un-sprayed Semigloss test strips have lost about 0.2 density units over a week or so. However, the sprayed one still has its edge over the un-sprayed test strip. With luck the sprayed paper will stabilize at about 2.2. In optimizing a curve for the Premium Semigloss paper, I find that I need to "under-print" the black ink with the "color" inks. There is a reason the C82 does this. My dmax is actually higher and the differential gloss of the 100% and 95% black patches is greatly reduced when I have one or more of the inks start at other than (0,0). My current neutral curve starts the blue curve at (0, 16) and the red curve at (0, 10). It is very difficult to see the differences in these dark tones. A difference of 0.15 can barely be seen when looking at 2.4 and 2.25 side-be-side. I think visually setting the level of the 95% and 90% patches is going to be more useful than the densitometer. The 95% is currently under 2.0 (with an initial 100% of up to 240 - but the printer is inconsistent there, and these high dmaxs don't stay there). I may lighten the 95% patch even more. Paul www.PaulRoark.com <http://www.paulroark.com/> [Non-text portions of this message have been removed]