Digital BW, The Print

Peter Nelson wrote:
> --- In DigitalBlackandWhiteThePrint@yahoogroups.com, Ernst Dinkla 
> <E.Dinkla@c...> wrote:
> 
>>Peter Nelson wrote:
>>
>>>--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Paul 
> 
> Roark" 
> 
>>><paul.roark@v...> wrote:
>>>
>>>
>>>>>>...Ironically, the smaller the particle, the
>>>>>>larger the surface area to volume ratio is.  This larger
>>>>>>surface-area-to-volume causes faster oxidation, which is the 
>>>>>>cause of most fading.
>>>
>>>
>>>Oxidation is a chemical process, not a physical one, so why 
> 
> would 
> 
>>>the surface area to volume ratio matter?    For a pigment 
> 
> particle 
> 
>>>to fade only the molecules at the surface need to change 
> 
> color.   
> 
>>>The fact that a faded pigment molecule on a small particle might 
>>>have a zillion unoxidized molecules underneath it and one on a 
> 
> big 
> 
>>>particle might have TEN zillion unoxidized molecules underneath 
> 
> it 
> 
>>>doesn't seem all that significant since it's only the one on top 
>>>that we see, unless you're implying that the molecules have 
>>>motility.  (are you?)
>>
>>I agree with most of what you write but the assumption that the 
>>pigment particles in inkjet inks are opaque, inkjet pigment inks 
>>are opaque and inkjet pigment ink layers are opaque isn't 
>>correct.  If you accept that they are all more or less 
>>transparent then it isn't just the top of the ink layer that does 
>>the coloring, it isn't just the outer molecule layer of the 
>>particle that does the coloring but also the mass of the pigment 
>>particles. 
> 
> 
> Whether or to what degree it's transparent is pure speculation, as 
> is the mechanism of its transparency.  Keep on mind that individual 
> molecules are much smaller than a wavelength of light, so the actual 
> color you see is based not only on the structure on the individual 
> molecule (e.g., its chromophore) but also on its solid state 
> properties, such as whether it's in a lattice or layers or whatever, 
> and finally its dispersal within a medium or vehicle.   It might be 
> transparent to certain wavelengths based on its chromophore, or it 
> might be transparent based on particles being so widely dispersed in 
> the medium that most of the light landing in the ink never hits any 
> pigment until it gets much deeper into the medium or vehicle.   
> Since we have no idea what the chemical and physical properties are 
> we cannot speculate about how transparent the pigment might be, or 
> why.

Subtractive color mixing doesn't work without some transparency 
of the individual ink layers. It's gamut increases a lot with 
high transparency. It would be impossible to get the gamut of 
inkjet pigment inks without transparency. That part at least 
isn't pure speculation.

If the coloring only is a result of the reflectance of the 
surface of the particles and the transparency of the inklayer is 
just the path between the particles to the substrate and back 
then the coloring should increase with the total particle surface 
increase of the smaller particles compared to the bigger 
particles. In that case you could use less total particles volume 
to get the same coloring effect. What I have learned on pigments 
is that it doesn't work like that. If the particles get too small 
they don't have the same coloring effect. Probably related to the 
solid state properties of the particle, breaking up the 
structure. Is probably different with those dye based organic 
pigments but my bet is that they are much more transparent than 
opaque anyway.

Interference and diffraction. I find both pure speculation with 
little reference to inkjet practice.The dispersal within the 
medium as the factor for coloring would immediately create 
problems in immense differences on different substrates. There's 
very little medium left in the printed inklayer, one of the 
bigger problems in inkjet printing. The same for layer forming on 
the surface.  BTW, the interference coloring would only work 
nicely with some transparency of the layers.

The speculative part works on both views, in your assumption of 
opaque particles, on my assumption of transparent particles.


> 
>>Then the total surface of the particles to the total 
>>volume of the particles plays a role in the fading properties. 
>>The larger total surface of the smaller particles will react 
>>faster to any possible reagent and so more molecules of the mass 
>>will loose their unique coloring power faster and become 
>>something else, it isn't that important if the shift occurs in 
>>tone, hue or saturation, it is a shift.
>>
> 
>  
> 
>>Surface area to volume area matters a lot in a chemical process. 
>>Adding fresh aluminium powder to firework certainly gives more 
>>reactive effect than adding an aluminium slab.
> 
> 
> Sure, but we can only say that because we know what the physical and 
> chemical properties of firework propellants are.  We know that it 
> proceeds faster when a larger surface area of the propellant is 
> exposed to air because we know that a rapid exothermic reaction with 
> the oxygen in the air is the basis of the reaction.   Since we don't 
> know anything about the chemical or physical properties of inkjet 
> inks we're just BS'ing when we speculate about the chemical process 
> by which they fade.   It may not even be a reaction with air, and if 
> it is it may only be facilitiated by special conditions such as UV, 
> certain ions, or whatever.

According to Wilhelm oxygen and ozone and probably some nitrogen 
related gases are a cause of fading in dyes. If the paper coating 
(gelatin, PVA) embeds the dyes or pigments properly (lowering 
humidity changes + oxygen penetration) then that process will be 
slower. If the pigment particles are coated with a polymer like 
acryl a similar protection can be achieved. That's what Epson has 
done with the encapsulated particles. Any printing on mat open 
structure coating papers like the Hahnemuhle papers ends in 
pigment particles being quite exposed to the elements with little 
medium left around them or only relying on the encapsulation + 
some medium left.

>>The color pigments of inkjet inks are much more related to the 
>>dyes that are also used in inkjet inks than to the opaque 
>>"grinded rock" mineral pigments.
> 
> 
> Do you know that for a fact?    Can you cite references or sources?

There's just no mineral with the staining power needed for CMY 
subtractive printing, this is all artificial/organic stuff for 
ages, at least for the time that CMYK printing has an acceptable 
gamut. 1920's is my bet.  Dyes are possible too and were/are used 
in roto gravure, flexography. Not handy in offset due to the 
water/oil balance needed in the process.

There's a good research report in PDF done by a German lady that 
is somewhere in the RIT archives though I did see it before on a 
German site. Will try to find that again. That's not the only 
source I have that information from.

Well not the German lady but this time a German lad:

http://www.knaw.nl/ecpa/PUBL/InkJ-144.pdf

Search for pigment in that document.

Any Google search on    organic pigment dye inkjet fading    will 
deliver something accordingly.

http://www.rit.edu/~661www1/sub_pages/inkjet_stability_72dpi.pdf

That's Barbara Vogt at last.

Whether this all is relevant for the carbon pigment particles in 
quad inks has to be seen. At least it is relevant for the toners 
being dye, high gamut organic pigment or low gamut/slow fading 
pigment.

Ernst