Re: (Gum) Tonal scale

On Dec 7, 2005, at 5:01 AM, Tom Sobota wrote:

>
> Clerc, in his 'Photography, Theory and Practice' (I have the second
> edition, translated to
> English in 1930) speaks about the 'Law of Densities':
>
> "... This fact is generally expressed by saying that the quantity of
> absorbing material (the
> mass of reduced silver per unit area in the case of a photographic
> negative) is proportional
> to the logarithm of the opacity. The name 'Optical Density' is given
> to this value ...'

  I don't have the energy at the moment to go into the
opacity/transparency thing. But I'll just say at the moment that not
only is there not the direct relationship between the (distribution) of
  the product of exposure and the darkness of tone for gum that there is
for silver, (which you've so thoughtfully shown above) but the law that
relates opacity to the darkness of the tone doesn't work in gum the way
it works in silver. In gum printing, a tone can be very dark but also
transparent. If you're interested, look at the discussion about opacity
and transparency on my pigment page, and see the chart which shows
opaque pigments on one side and transparent pigments on the other,
going all the way to a black which Photoshop calls 100% black.

I am exceedingly weary. I've kept with this because I think that while
it's a narrow point, it's a point which can be useful in understanding
the gum process. This thought is supported by private notes I've
received from folks who have said it was a revelation to them, and
helped them understand why they couldn't calibrate their gum exposures
the way they had expected to be able to.

>
> Agreed. And Phil Davis, in his 'Beyond The Zone System' clarifies the
> matter even more (I am
> back-translating from my Spanish version):
>
> 'The term "density" has a specific meaning in photography. By
> definition, the density
> is the logarithm of the opacity, which is the inverse of transmittancy'
>
(snip)
> Mind you, I understand what you're talking about, or at least I
> _think_ I understand, but Adams
> or not Adams, I still think that you should be using some other term
> for what you call 'density'.

I'm not the one who brought the term "density" into this discussion. I
would prefer not to use the term at all, because it has specific
meanings in silver photography that don't apply in gum printing, which
was, as I keep saying, the ...............point.
Katharine
Received on Wed Dec 7 09:45:59 2005