Re: Epson R2400 inks density - DISCLAIMER

[Alberto Novo <alt.list@albertonovo.it>]

> Alberto,  
> What conclusions did you come to from the data?  It wasn't clear to me.
I decided to obtain a full specrum of the absorption of my printer's inks in 
the range from UVA (320 nm) to visible (900 nm), in order to have a 
numerical basis for reasoning about the -supposed- relation between visible 
colour and UV absorption. The absorption spectra of the fundamental colours 
(Y, M and C) and of the secondary colours (R, G and B) show (with my Epson 
R2400 printer on Pictorico) that the UVA inks absorption is in no relation 
with the corresponding visible absorption. This was not proven before, but 
only hypothesized and variously argumented.
In particular, (again: with my printer, inks, etc.) in the *near 370 nm 
region*, which is the most representative for iron and dichromate processes, 
the most absorbing hues are green, followed by cyan and black. This last 
measurement confirmed me what I observed when printing the colour patches 
test, and at first it was really strange, that is that the black ink was 
less absorbing than a green shade.
The less absorbing inks are magenta, red and yellow. 
I strongly recommend to perform a similar analysis, which can only be done 
with a spectrophotometre and not simply a densitometre (which gives an 
integrated value over a not ever clearly defined wavelength interval), in 
order to characterize printers inks different from R2400 ones. General 
conclusions cannot be drawn from the spectra I have posted because they are 
R2400 specific (if not experimentally proven analyzing other inks).
Moreover, knowing the absorptions of the inks is only a first step towards 
the knowledge of their behaviour, because they need to be compared with the 
photon yeld range of the specific process, the emission spectrum of the 
lamps, and the filtering effect of other compounds present in the sensitive 
formulation. 
Alberto