Digital BW, The Print

I think the experience I have had over the last couple of days may be
relevant here.  My previous work with glop was using it with QTR during the
original ink lay down - "glop in the mix" so to speak.  Over the last two
days I have been working on a colour image with substantial areas of B&W (a
landscape where I have overlaid a channel mixer B&W layer but set the
opacity to 75% so that the foreground has colour but the mountain ranges,
sky and clouds are essentially a black and white image).  So the original
image was printed on Epson Premium Luster with the Epson driver and I have
been using QTR to overcoat the image with glop.

The uncoated image has all the usual bronzing issues especially in the
clouds.  A straight 15% (ex white) glop coating significantly reduced but
did not kill the bronzing.  I then used a glop curve that more closely
resembled the sort of curve I was using when glop was in the mix.  The toner
curve begins at (0,15%), climbs rapidly to peak at (20,75%), declines
steadily to (75,20%) and then to (100,15%).  This eliminated the bronzing
subject to my comments below.  To be clear, I send the Adobe RGB image to
QTR which gets converted on-the-fly to greyscale and the relevant glop
amount deposited according to the on-the-fly conversion.

But there are other issues.  It is very difficult to align the Epson print
with QTR - they each have slightly different paper sizes. (Unfortunately I
am trying to get a Super A3/B image done!)  My last test has a misalignment
of about 2mm.  As a result I can clearly see the shift in glop application
and, especially looking around the edges of the clouds, see where the glop
missed the cloud and hit the black sky.  I can also see the bronzing left
where the glop did not hit in sufficient quantity.  Where the extra glop has
hit the black or darker shades of the print there is a noticeable punch in
density and possible sheen difference (especially under halogen lighting).

So over-coating with a variable glop application may be susceptible to
aligning the two print runs.  Obviously this would be easier if both images
were printed using the same driver.  I think the peak bronzing problem area
is around L values of 70-90 and I guess that is where the LK comes into
play.

I would be very interested if someone with an R800 can print a B&W image
with lots of clouds against a very dark sky using the colour driver (not
black) and tell us whether the print exhibits bronzing (don't worry about
metamerism) without glop and then with glop, as the R800 does not have an LK
ink.  (I would be happy to provide a jpeg of the image I am playing with.)
I would also love to know the density difference between a glopless black
patch and a with-glop black patch.

Cheers

Steve