[pure-silver] Re: History... Clarification
- From: Jean-David Beyer <jeandavid8@xxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Mon, 19 Oct 2009 06:27:32 -0400
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Ray Rogers wrote:
| --- On Mon, 10/19/09, Jean-David Beyer <jeandavid8@xxxxxxxxxxx> wrote:
|
| " A very few are interested in Lippmann color photography. A very few are
| interested in making the little dots for half-tone photography (I have
| done it with ruled glass crossline screens generously donated to me by
| Max Levy & CO of Philadelphia, the very company that made screens for
| F.E.Ives way back when."
|
| Well, I would be very interested in both, particularly the former, but
| your results with the latter sounds interesting as well!
As I said in the private e-mail,
I never worked on non-Lippman plates. That was my great-grandfather,
F.E.Ives who did that. He made plates because he preferred the ones he made
to those he could buy. His were panchromatic. Also, when making half-tones,
he needed lithographic plates, and there were no such things, so he figured
out how to make some very high contrast ones, and devised means to intensify
the ones he got to obtain even greater contrast.
http://www.nndb.com/people/955/000167454/
I never investigated that. I am not a photo researcher. My grandfather,
H.E.Ives did that. He published that in _The Physical Review_ in 1907. He
published more in _Astrophysical Journal_ in 1908, "An Experimental Study of
the Lippman Color Photograph" and briefly summarizes it in his Rumford Medal
Lecture in 1951, "Adventures With Standing Waves".
http://www.nndb.com/people/456/000169946/
As far as half-tone work is concerned, What I do is put a negative of what I
want in my enlarger, and a sheet of Kodak Ortholith in my enlarging easel. A
small distance above the Ortholith I place a glass sealed half-tone screen.
I set the aperture of the enlarging lens to what I need, depending on the
screen ruling, screen height, and the negative contrast, and set the
exposure time to get a
proper exposure. If I wish to burn the highlights, I stop the lens down and
expose some more. With the lens stopped down, it will give additional
exposure to the highlights, but will not expose the shadows any more.
I then develop the Ortholith normally, which in this case is in Kodak's
Ortholith developer. This looks good to the naked eye, but is not very good
as the dots are called "soft." So I contact print that to another sheet of
ortholith to get a hard-dot positive. If that is what I want, I stop there.
If I want a hard-dot negative, I contact print that a second time. Whether I
want a positive or a negative depends on the plates required for the press I
will use.
What the half-tone screen is can be described as follows:
Take a piece of glass and rule parallel lines on it with a ruling engine,
something like what is used to make a diffraction grating. Make the lines
and spaces between them of equal width, and fill in the ruled lines with
black opaque stuff and clean off the un-ruled area. Do this with another
picee of glass and mount them at right angles to one another. I am pretty
sure they are glued together with something like Canada Balsam. The thing is
then held more firmly together with a frame of aluminum. You get a lot of
little square holes. I have two of these screens (about 8" x 10") donated by
Max Levy & Co of Philadelphia who made the screens for my great grandfather
over a century ago. One is ruled 65 lines per inch and the other is ruled
150 lines per inch.
If you put this in the optical path between the enlarger lens and the
ortholith film, each hole in the screen is a pinhole, as in a pinhole camera
and it makes an image of the aperture of the enlarging lens, and the
intensity of the light is proportional (inversely) to the density of the
corresponding part of the negative above the lens. Now since there is lith
film under the screen, only the brightest part of the transmitted light will
develop. In my case, the aperture diaphragm is circular, so I get round dots
whose diameter is proportional to the light intensity. So if a lot of light
comes through, I get a big dot, and if little light comes through, I get a
little dot. You should be able to figure all this out if you think about it
a while.
|
| "I do not know if you propose to send me personal information that you do
| not want seen by the list, but if that is the case, how do you know I am
| trustworthy to keep it secret? And even then, you would have to consider
| sending it to me encrypted."
|
| Ha! I endevor to live my life in such a way that secrets are unnecessary.
| Unfortunately, it never ceases to amaze me how the simplest truth can be
| used so effectively as a weapon. Ever have an argument with a loved
| one?!! Oh well....
|
I guess not. I have had disagreements upon which we have never come to
agreement once in a while, but never arguments.
- --
~ .~. Jean-David Beyer Registered Linux User 85642.
~ /V\ PGP-Key: 9A2FC99A Registered Machine 241939.
~ /( )\ Shrewsbury, New Jersey http://counter.li.org
~ ^^-^^ 06:00:01 up 18 days, 14:59, 3 users, load average: 4.73, 4.44, 4.31
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