The backside of my Epson HPn has about the same Lab B as the front. They do say to print on only one side, however. Back-side coatings are to control curl.
The less expensive spectros are not very accurate when it comes to the Lab A & B. What I've found works best with my Spyder is to first Calibrate it, then immediately measure any random mid - Lab L paper (like an orange post-it on my desk), then immediately calibrate it again. In short, I think the unit responds to being warmed up a bit. Then before I make a read of a 21-step, I again read the post-it a few times, then enter the "Export to" info and do the 21-step read. I'm getting much more consistent results this way.
Also, of course, the calibration tile needs to be cleaned occasionally, and the end of the spectro needs to have the rubbed off carbon from the read rubbed off on a paper (like the margin of the paper just read) every time. Otherwise some of it is going to be transferred to the calibration tile.
When I look at the graphs, it makes the most sense to draw (mentally) a straight line between the paper white and the 100% black. The extent to which the Lab B varies from this straight line is a more accurate way to compare relative warmth than to just look at the absolute numbers.
The companies involved have been alerted to the issue. I would expect a few days of their exploring their ends might be needed.
Paul
On Mon, Feb 1, 2016 at 2:11 PM, phlg@... [DigitalBlackandWhiteThePrint] <DigitalBlackandWhiteThePrint@yahoogroups.com> wrote:
Will,Epson claims the Hot Press Natural is coated on both sides, so there is no wrong side, even if they are slightly differents. But good idea to check the other side, I always print on the smoothest.