U of S | Mailing List Archive | alt-photo-process-l | Re: separations for gum printing

Re: separations for gum printing

I am old book on the colour printing:
Livre d'origine dans un état impeccable d'Alcide Ducos Du Hauron
"La Photographie des Couleurs" et les découvertes de Louis Ducos Du Hauron suivi d'un manuel pratique, collection A L Guyot

Le livre d'origine dans un état impeccable " La Photographie des Couleurs" par impressions pigmentaires superposées, procédé détaillé d'impression au charbon en plusieurs couleurs superposées pour photographes amateurs et professionnels de Léon Vidal, Editeur Charles Mendel

Le livre d'origine dans un état impeccable " Traité Pratique de la Photographie des Couleurs" par L Dugardin Editeur Société Int de la Photographie des Couleurs

Atelier Noir de Faire

----- Original Message -----
Sent: Thursday, November 20, 2008 7:52 PM
Subject: separations for gum printing

This recent discussion on tricolor gum printing sparked my interest. My printing times are about the same with all colors, but perhaps I compensate with development time, these two variables are related. But that is not what I wanted to discuss. Mostly everybody agrees that B channel (in the RGB color space) intended for yellow printing always requires a different curve then RG channels. This is also my observation and practice. The B channel is almost always much 'flatter" then oher channels and requires a more pronounced curvature. Quite frequently I do not have enough definition in the B channel to get enough contrast resulting in prints with overall yellow cast.
Since CMYK space and separations are intended for printmaking, which is what we do in gum I started making CMY separations with K set to zero. There is a visual difference on how the pictures look on screen in these two color spaces (anyone interested should try to toggle between spaces in Photosop) and also how the Y separation looks compared to B channnel in RGB color space. It also seems like the colors are less muddy. I have only done a few pictures so far, but I want to see if anybody is doing different methods of generating separations for tricolor gums.

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