From: Jim Morris (jmorris@morriseditions.com)
Date: 09/11/02-11:00:59 PM Z
Perhaps, against my better judgment, I will take a stab at this. Could
it be that the confusion is due to the different use of the term
"opacity" viewed from a scientific stand point verses the artistic
stand point? Many painters might consider "opacity" to mean, for lack
of a better definition, covering power. In other words, if I paint a
piece of paper with a dye based ink - let's say cyan- I can achieve a
deep cyan color but I would also be able to see the characteristics of
the paper on which it was painted; on the other hand, if I paint the
paper with white latex paint, the paint may completely obscure the
surface of the paper underneath becoming a new surface itself. In this
case, if we were to define "opacity " as "covering power", the latex
paint would be lighter and more "opaque" while the cyan ink would be
darker and more "transparent".
Yes, no, maybe?
Jim Morris
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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