Digital BW, The Print

Paul,

It becomes a journey between Scylla and Charybdis if you want to avoid 
gloss difference, bronzing, color inconstancy and lay no restrictions on 
the viewing conditions.

It now looks like all the dyes types have issues with color constancy in 
monochrome prints, more than black pigments have. LEDs and CFLs are not 
without spectral pikes. The question is whether the higher transparency 
of dyes and by that the kind of reflective filtering plays a role 
compared to carbon pigments or whether the black dye colorant spectral 
reflection is irregular. You could check a spectral plot of the dye made 
with a normal (non UV-cut) spectrometer. The smallest wavelength 
interval measurement for an Eye1 Basic would be possible with ArgyllCMS. 
You might need a spectroradiometer to locate smaller deviations in 
spectral reflectance, absorption, transmission. I think that is the 
basic approach to tackle color inconstancy at the print side. You have 
to find a neutral medium to print the colorants on. Yes it would be nice 
to check the carbon pigments too then and your ink mediums.

You did not mention the paper you used. OBAs remain an issue anyway but 
I guess that the different filtering of dyes compared to the more opaque 
carbon pigment enhances the OBA effects. If carbon pigment was totally 
opaque the color mixing of greys (black + paper white) could actually be 
called additive. Transparent black dyes + paper white still have a 
subtractive color mixing base and all the irregularities in light 
transmission + reflection of both are added to one another. The more 
continuous and flat the spectral reflectance of the paper white is, the 
less the colorants different transparencies affect the reflectance of 
grey area. That said if the dye itself is not showing an irregular 
spectral reflectance, including fluorescence. Carbon pigment will not 
show fluorescence and will suppress possible fluorescence in the other 
components by absorbing UV and what is emitted in energy from 
fluorescents. TiO2 whitening agent in the paper could reduce UV excited 
fluorescence in other components of the print too as it absorbs UV and 
emits the energy beyond the visible spectrum.

White LEDs can be based on UV or Blue LEDs immersed in (yellow) 
phosphors. For normal lighting the RGB based White LEDs are too 
expensive. Next to spectral spikes there are other issues.  Some of that 
is discussed in a document that I have no link for, so do a google for: 
LpR10_Instrument_Systems_web.pdf  The Wiki pages on LEDs are good too.

Better wait for Quantum Dot LEDs if efficient, full spectrum lighting is 
needed. Till then halogens are best.


-- 
Met vriendelijke groet, Ernst

Dinkla Grafische Techniek
Quad, pi\ufffdzografie, gicl\ufffde
www.pigment-print.com