Re: Gum problem(s)

Yes, by all means test it for yourself. However please keep in mind that
this was only said and meant as advice for a beginner.

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.

"Who says" you ask. To tell you the truth I don't remember. I read it in
a couple of different places years back. When I find it again I will tell you.
Anyway it has been useful for me in a time long before Internet, when
there was nobody to ask.

What is important is perhaps not this test but the fact that the coat should
be rather thin and keep a certain transparency at all times. This fact is well
attested in the bibliography:

"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.

Tom

At 21:53 18/11/2005, you wrote:
>Second thought:
>I sent something through a while ago, questioning the advice about coating
>so that you could read text through the coating. That post hasn't found
>its way back here yet, but I've been thinking more about what I said, and
>decided I don't necessarily agree with myself. After all, I've always
>been a great one for printing with transparent pigments, and no doubt you
>can see the previous print through subsequent coatings on a tricolor
>print, even (very dimly) the cyan layer which for me goes on last. Even a
>very dark color that's transparent, say ivory black, is transparent
>enough that I wouldn't be surprised if you could read a newspaper through
>it, even though it can print as dark a value as lamp black can.
>
>In my previous comment, I was think not of transparent layers but of a
>coating intended to produce a one-coat print, like lamp black or a
>blue-black or brown-black that you might use for this purpose, and I still
>wonder about that, but like I said, I'd have to try it for myself.
>kt
Received on Fri Nov 18 18:54:43 2005