Re: Gum problem(s)

I'm glad that you too have read it somewhere, Judy. I couldn't believe that
I'd be the only one...

I cannot tell if they really did it or not. But why not? It's so easy ...

What I _did_ tell is that I tried it and found it useful. For me, that is.

But I see that I did not express myself clearly as to the procedure. The
idea is to spread a little of the gum/pigment/dichromate on a real
newspaper, with a finger perhaps, let it dry and then verify if the
written text on the newspaper still can be read or at least still can be
seen through. Only then, after perhaps adjusting the pigment content in
your mixture, you coat the definitive paper.

Attempting to read a newspaper through a coated paper would have been
impossible even for Demachy, I think. And futile, in a way, because the
whole purpose of the test is to verify the transparency of the mixture
before coating, not after.

Nothing that could not be done today with a densitometer, a photometer or
even a simple photocell, by the way.

Tom
P.S. Sorry but I cannot understand the meaning of 'but I suspect that the
idea suffices'. 'suffices' as in 'sufficient'? You mean that 'the idea is
enough'? Please keep in mind that I'm one of those on this list that you
was speaking of the other day: English is only my fourth language :-)

At 07:02 01/12/2005, you wrote:

>On Sat, 19 Nov 2005, Tom Sobota wrote:
>
>>Beginners, and I was no exception so I know, mostly tend to coat too
>>heavily. In this context, the "newspaper test" is useful, I think.
>
>A propos of that newspaper test -- yes, I've read it in several old
>manuals & articles. But IF they really did it then, I think we'd have to
>modify the operation to do it now.... because the papers we use are so
>heavy that even with the brightest light under them and no pigment I doubt
>we could read much if any newsprint through them.
>
>Demachy & co printed on a paper called cartridge paper, or like that --
>about what we'd call typing paper today.
>
>So you could coat your emulsion onto typing paper and give it the
>newspaper test, but I suspect that the idea suffices.
>
>J.
>
>
>>"If the coating appears to be dark enough to completely hide the paper
>>from view, then it's either too thick or too much pigment has been used."
>>("Historic Photographic Processes" , Richard Farber, 1998)
>>
>>"The paper is covered with a thin coat of this mixture, so that the paper
>>can still be seen through the color..."
>>("Manuale prattico e ricettario di fotografia, Rodolfo Namias, 1914)
>>
>>"Dieselbe (die Mischung) muss so dünn aufgestrichen werden, dass
>>das Papier noch durchscheint..."
>>("Das Pigmentverfahren, der Gummi-, Öl- und Bromöldruck und
>>verwandte photographische Kopierverfahren mit Chromsalzen"
>>Josef Maria Eder, 1917)
>>
>>and many others. The "newspaper test" is only a simple method to
>>check the transparency of the coat before applying it.
>>
>>But I think that it was originally meant for checking the dark colours
>>usually used for one coat printing. The transparent colours used for
>>trichromy are ... well ... transparent.
Received on Thu Dec 1 04:41:18 2005