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

Re: Epson R2400 inks density

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.
The values on the vertical axis (A=Absorbance units, where A= -log10(I/I0), I=intensity of the incident light, I0=intensity of the transmitted light; the absorbance is proportional to the concentration of the absorbing specie in a sample) are the densities of the inks without the base density of Pictorico at every wavelength.
That is, A has been measured using Pictorico+ink in the analysis beam and Pictorico only in the reference beam.

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.
In fact, this was a spectrophotometer, an instrument used in a chemical lab. You cannot make the same measurements with a densitometer.
I wanted to analyze the inks in this way because of the debate about the comparison between visible hue and UV absorption. Yhe most interesting part of the graphs is indeed that extending from blue to UV. The absorption of Y confirms what I previously thought, that some absorption of the yellow would have been also towards the very near UV, but nobody knew (or would have predicted) exactly its behaviour.
Science needs measurements, not argumentations.
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
I have put the 370 nm line as a reference to favour the comparison among the inks. It is true that many processes are sensitive in this range, but I have not yet found any number in this regard.
These graphs should be compared to the light spectrum of the lamp and the absorption spectrum of the process in order to calculate the "efficent" wavelength range.