U of S | Mailing List Archive | alt-photo-process-l | Re: Epson R2400 inks density

Re: Epson R2400 inks density

Okay, if I'm reading this right, Clay's graphs show how UV absorbence of one narrow spectral region varies as the amount of ink varies, in other words the amount of ink is varied and the wavelength (s) measured is constant. Alberto's show how UV absorbence varies across wavelengths, holding the amount of ink constant. Yes?

On Apr 29, 2009, at 2:54 PM, Clay wrote:

My measurements were made with a 361-T, which supposedly measures UV in the 380 nm range
On Apr 29, 2009, at 4:10 PM, Don Bryant wrote:


Thanks for posting this. I don't use a 2400 but I still find the results of
the analysis interesting.

I assume the values labeled on the vertical axis A represent the UV log
density of the ink plus base density of the Pictorico substrate.

How were the patches measured? That is what instrument was used? I should
fire up my UV densitometer and do the same with my printers. Since you have
plots extending across a broad spectrum in the 300 to 900 nm range I assume
it's not likely you used a UV densitometer like the xRite 361T which is what
I have.

I know Mark Nelson has graphs of UV ink density published in his PDN eBook
and Clay Harman has recently contributed some measurements with a couple of
Epson printers, but I don't think those measure the same spectral width you

I also noted the 370 nm axis and I assume this is considered the mid-point
for the range of UV frequencies that alt processes tend to be most sensitive

Great work,

Don Bryant

-----Original Message-----
From: Alberto Novo [mailto:alt.list@albertonovo.it]
Sent: Wednesday, April 29, 2009 4:52 PM
To: Alt-Photo Mailing List
Subject: Epson R2400 inks density

A week ago I gave to a friend of mine a print of YMCK and RGB patches (Epson

R2400 on Pictorico) for an analysis of their UV-VIS spectra, and now I have
the results. The graphs are posted in

What can be seen is that in the 320-400 nm region (UVA), the yellow ink
absorbance abruptly falls from about 3.6 at 400 nm to its minimum at about
440 nm (A=1.5).
The other inks have a neatly different behaviour, with an absorbance rising
when going from 400 to 320 nm. The most dramatic change happens with magenta

and cyan, which have an absorbance of about 0.75 @ 400 nm and respectively
3.2 and 3 @ 420 nm.
The absorbance values of red, green and blue are not simply the sum of the
primary (CMY) colors at a given wavelength, but can be roughly approximated
if the sum is multiplied by 2/3 (see for example the curves of C, B and G,
the last two being C+M and C+Y, in the 600-750 nm region).
Moreover, the absorption of 50% saturated color patches (i.e. R=255, G=255,
B=128 for a 50% Y), that one likely thinks they should have 50% absorption
of the full strength ones, are three or four times lower (not shown in the