From: Katharine Thayer (kthayer@pacifier.com)
Date: 09/12/03-03:11:59 AM Z
This is just further confusing the matter. Look, you guys are making
this much more difficult and complicated and technical than it needs to
be. The fact is that gum printers use the word "density" to mean a
dark value, even though it doesn't work the way it works in silver,
where the denser the silver, the more opaque the material is, the darker
it is. Judy suggested we should probably switch to "DMax" for this
discussion to avoid confusion, and perhaps I should have stayed with
DMax rather than getting everyone's knickers twisted by staying with the
word "density."
But the original question was what pigment would have enough DENSITY for
a one-coat gum, and whether gouache was the best way to go. My answer
was that it depends on taste, whether you want an opaque print or a
transparent print, since gouache is opaque and has a different quality
than transparent watercolor. My whole point was that a paint does not
have to be opaque to be very dark in value, and that point remains. The
formulas are true in their place but irrelevant to this discussion.
Katharine
Sandy King wrote:
>
> Thanks Greg, you are absolutely right. This exchange has been very
> hard to follow because of the obvious confusion of terms. Density is
> the common log of opacity, which merely means that we are using a
> numerical shorthand to express opacity. Some may be confusing opacity
> with transmittance, but these are different, though related, in that
> opacity is the reciprocal of transmittance.
>
> For example, a material that has a transmittance of 20% has an
> opacity of 5 and a density of log 0.7. A material that has a
> transmittance of 50% has an opacity of 2 and a density of log 0.3.
>
> Sandy
>
> >Sorry, but I can't keep my fingers off the keys. There is no
> >difference between "density" and opacity. Go back and have a look at
> >your textbooks. I think somebody already pointed out the relationship
> >of opacity to density. Varying degrees of "opacity" are equivalent to
> >varying degrees of density they are just expressed (mathematically) in
> >a different fashion, but only if you're dealing with densitometry. Do
> >you really thing about "density" when you photograph a tree?
> >
> >I think the confusion may stem from confusing methods used to read
> >reflected density (reflected light actually) and transmitted density?
> >It is possible that no light is making its' way to the paper, but
> >rather that light which strikes the pigment is being reflected back
> >from the pigment (hint - stop thinking in terms of gelatin/silver
> >processes). Correct me if I'm wrong, but I think what Katherine means
> >when she uses the term opaque is that no light is being reflected from
> >the paper base, but rather the light is being reflected back from the
> >surface of the pigment. A warning to those folks versed in
> >Sensitometry - color densitometry is much different than B&W and
> >colorimetry even mores so (IMHO :*).
> >
> >-greg schmitz <gws1@columbia.edu>
> >
> >
> >
> >
> >==================
> >
> >All of our current environmental problems are unanticipated harmful
> >consequences of our existing technology. There is no basis for
> >believing that technology will miraculously stop causing new and
> >unanticipated problems while it is solving the problems that it
> >previously produced.
> >
> > Prof. Jared Diamond, UCLA
> > Harper's Magazine, 2003 June
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