Digital BW, The Print

--- 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.

> 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.

 
> 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?