Re: (Gum) Tonal scale

Yves,
Is it that we' ve simply misunderstood each other about the way we're
using the word "density"? When you spoke of reading tone from a graph
relating response to exposure, (density) to amount of exposure, I
assumed you were using the word "density" to mean "density of reaction
product," since when I think of "response to exposure" I think of the
chemical reaction that is the direct response to exposure. In silver,
exposure causes the production of a silver compound; the density of
that compound is directly related to tone. The tone IS the compound,
in a directly quantifiable sense. I was simply making the point that
it's not that simple for gum.; in gum the tone is not made up of the
material that results from exposure, and the relationship is not so
well known.

 From this post (below) that I got just this morning, it seems that when
you used the word "density" you simply meant "tone" not density of
reaction products. You just meant that the tonal scale means the
difference between the lightest and darkest tones, which is what I mean
by tonal scale. But your use of the word "density" threw me off.

P.S. I sent a post to the list this morning that came back to me in 2
minutes, so I thought maybe the problem with the server was fixed, and
I wrote two or three more posts. But now it's five hours later and none
of those have come back, so it's fairly obvious that it's still not
behaving properly.

Katharine

On Dec 6, 2005, at 10:46 AM, Katharine Thayer wrote:

>
> On Dec 3, 2005, at 12:16 PM, Yves Gauvreau wrote:
>
>> Katherine,
>>
>> You know the difficulties english gives me and I'd like to know if I
>> read
>> you correctly this time.
>>
>> The way I read it, you basically say that because the stuff we put on
>> the
>> paper in gum prints is different then what is used in carbon,
>> cyanotype,
>> kalitype, platinum, silver, tempera and probably most other types of
>> prints
>> that we can't establish a quantitative or even a qualitative relation
>> between a certain given amount of light and a tone on the paper using
>> a
>> measure like the optical density of this tone.
>>
>> Is what I said here essentially the same as what you have been saying
>> all
>> along???
>
> Hi Yves,
> No, that's not what I'm saying at all. I'm not saying that we can't
> establish a relationship, (for any specific pigment/gum/dichromate mix
> under conditions where all other variables are held constant) between
> a given amount of light and a tone on the paper. I've said again and
> again that certainly we can do that.
>
> What I am saying is that because of the nature of crosslinked gum,
> and because so little is known about the mechanisms of the process for
> dichromated gum in general, we can't establish a relationship between
> exposure and density of crosslinked gum nor can we establish a
> relationship between density of crosslinked gum and tone. And perhaps
> I should emphasize here that when I say "density of crosslinked gum"
> I'm not talking about tone, I'm not talking about optical "density,"
> because this material has no tone by itself; it's colorless and
> transparent; there's no tone to read the optical density of. I'm
> talking about the actual density of the crosslinked gum, the
> proportion of the layer that's crosslinked. Luckily it doesn't matter
> that we don't understand that intermediary relationship, because the
> only relationship we need to understand is the relationship between
> exposure and tone, which is unique for each pigment/gum/diichromate
> mix in each unique environment of materials, equipment and atmospheric
> conditions, and which we can graph without knowing the actual density
> of the reaction product.
> Katharine
>
>
>
>
>> ----- Original Message -----
>> From: "Katharine Thayer" <kthayer@pacifier.com>
>> To: <alt-photo-process-l@sask.usask.ca>
>> Sent: Saturday, December 03, 2005 1:57 PM
>> Subject: Re: (Gum) Tonal scale
>>
>>
>>>
>>> On Dec 1, 2005, at 11:02 PM, Judy Seigel wrote:
>>>
>>>>
>>>> On Thu, 1 Dec 2005, Katharine Thayer wrote:
>>>>
>>>>> ... My point about the unpigmented gum was to emphasize that while
>>>>> the pigment does provide the tonal scale, it does not participate
>>>>> in
>>>>> the reactions which constitute the response to exposure, so unlike
>>>>> silver printing and many other photographic processes, with gum you
>>>>> cannot draw a curve relating exposure to *density of reaction
>>>>> product* to tonal scale.
>>>>
>>>> Actually this calls to mind an expression I've used in trying to
>>>> explain the process -- I say the action is the gum, dichromate, etc,
>>>> and "the pigment is just along for the ride." But in fact, it
>>>> occurs
>>>> to me that the character of the passenger can make a large
>>>> difference
>>>> also -- if he weighs 300 pounds, if he keeps opening all the
>>>> windows,
>>>> if he throws rocks at the bicycles passing by, etc. (Or "she," of
>>>> course.) That is, we do know that the particular pigment affects
>>>> behavior -- even if just its opacity.
>>>
>>> Which is what I keep saying. Or maybe you're just writing to say you
>>> agree with me, but every time I agree with you, you write back to
>>> agree
>>> with me again, which makes me think that you think we are debating
>>> opposite sides of an issue. My whole point is that tonal scale is a
>>> function of pigment and pigment concentration, (mainly, but along
>>> with
>>> a host of other things) and so if everything else is held constant,
>>> every pigment and every concentration of that pigment will give a
>>> different tonal scale. Yes, pigment affects behavior, very very
>>> much,
>>> that's exactly what I'm saying.
>>>
>>> My whole point, and my only point, throughout this discussion, is
>>> that
>>> the relationship between tonal scale (since it is made of pigment
>>> which
>>> does not participate in the reaction) and response to exposure,
>>> (since
>>> it is the production of transparent crosslinked gum) is an indirect
>>> and largely unknown (in a quantifiable sense) relationship, and so
>>> can't be graphed to read tone from density of crosslinked gum, as
>>> someone wanted it to. How many times would I have to say that, I
>>> wonder, before people started understanding what I'm saying.
>>> Katharine
>>
>
Received on Tue Dec 6 14:40:52 2005