U of S | Mailing List Archive | alt-photo-process-l | Re: green-yellow

Re: green-yellow



I was setting out to try to explain how the HSL array works, and then
I realized that's a really silly thing to do, when Michael Koch-
Schulte has explained it so well himself, with many illustrations to
aid in understanding. Read this; I think it's by far the most
brilliant and lucid explanation that's ever been written about
digital negatives:

http://www.inkjetnegative.com/images/RNP/rnp.htm

Here's the HSL profile I get for gum, with my printer/inkset and
light source:

http://www.pacifier.com/~kthayer/html/HSL.kt.gum.html

You can see that you get white all across the spectrum, if you go
down far enough on the value scale. If you take a few selected
colors from one middling row of the array, which is essentially what
you're doing when you use the color patch things to determine
negative color, you'll get white for some and tone for others, but as
I've said, that doesn't really tell you much. The HSB-HSL approach
shows you exactly where white occurs for each of the hues across the
spectrum, at the optimal exposure for your emulsion, and it shows how
the tone decreases in value as the density increases: smooth and
even, or jumpy and grainy. To me, this approach makes eminent
sense. Everyone finds their own way that works best for them; this
what works for me.
Katharine




On Apr 13, 2009, at 12:59 AM, Alberto Novo wrote:


I have posted my bw paper example here for what it is worth
(apparently nothing to certain listees) for an illustration of
color under tungsten not UV light:
http://christinaanderson.visualserver.com/Text_page.cfm?pID=2448

As usual, I can speak only about my experience with my printer and
UV light source, but at first I confirm one of your observations:
the black of R2400 is not as UV blocking like other colors. This
fact can be added to the "nonsenses" about inferring UV absorption
exclusively on the visible color.

It is nonsense, but not to Twentysomethings :) But apparently
Loris, myself, and others find yellow in the Ultrachrome inks to
be the densest, whatever the reason if not its color (on 6
different printers for me, but all Epson) but that is not a
quantative fact, because it does not related necessarily to dye
based printers or HP printers...but it seems I should be careful
to "couple" its UV blocking nature to its color opposite the UV
spectrum as I think you are saying. I will stand corrected.

I have under my eyes the color calibration for kallitype, copper
print and oilprint. The first two have the whites printed in the
green/green-yellow region, say from H=127 (S and B=100) to H=87.
The third has the whites printed in the yellow region, from H=73
to 52.
So, iron and dichromate processes (with my printer, etc...) are
absorbing in different region. Nothing new...
One source of differences among observations might be the shape of
the absorption region of the inks, that of the sensitive compound
(iron, dichromate, silver...), and that of the UV emitting source.
All are more or less bell-shaped so that this mix gives back a peak
with its maximum in a different region of the spectrum. As I have
previously said, this is only a probable description which should
be confirmed by instrumental measurements.

4. Alberto, did you at all get affected by the earthquake? It
has been on the news lots here and I offer condolences.

Thank you, Chrstina. I live in Venice (and work in Milan) so I have
not been affected at all. The damaged region is up to about 50 km
from the epicentre, close to l'Aquila. There are at present 293
dead, about 1500 injuried and about 38,000 evacuees, with the need
of 5,000 temporary wood houses in the next three months.
It seems that suddendly we are remembering that most part of Italy
is sensitive to earthquakes:
http://zonesismiche.mi.ingv.it/mappa_ps_apr04/italia.html
though here and there the anti-seismic building laws have been not
applied by some builders in the last decades, and we cannot hope
that the ancient buldings (many of them a thousand of years old, or
more) can be resistant for ever.
Alberto