Re: gum prints on Yupo
Hi Keith, I have two different kinds of gesso. Both Daler Rowney brand, one System-3 white, the other is Cyrla black. System-3 white works well in terms of keeping the gum image (but still exhibit a chemical - not pigment! - general stain). Cyrla black reacts just as you describe and doesn't hold the gum image (even with added calcium carbonate) at all; as soon as you put the image in the development water, it leaves the substrate instantly (exactly as you experienced / showed in your first trial with Artboards gesso). I plan to change the gesso additive from calcium carbonate to silica fume -> hoping it won't react with dichromate but still provide tooth for gum emulsion... Better, I will look for proper flexible plaster -> for making "gum-o-fresco"s ;) Your gesso tests are beatiful / interesting! I liked most the last one... Regards, Loris. 3 Kasım 2008, Pazartesi, 7:26 pm tarihinde, Keith Gerling yazmış: > Loris, > > I have experienced a definite pigment stain with that kind of size - > an odd "solarized" look where the highlights stained and the midtones > would clear. A coat of hardened gelatin seemed to help. I wonder if > you observe the same effect as I do using a similar mix: when I brush > on the emulsion, I detect a very obvious separation where the surface > draws the dichromate away from the pigment. Initial brushstrokes are > very clearly orange and only with repeated brushing does the emulsion > seem to "come together". In my case the exposures are much longer, > but that may be due to the fact that I am using lampblack and it is > self masking. In any event, my normal exposure with 1 part gum to 1 > part saturated pot di is 8 minutes, and I'm having to use 20. > > Keith > > 2008/11/3 Loris Medici <mail@loris.medici.name>: >> I had encouraging results printing on yupo coated with acrylic gesso + >> calcium carbonate mixture. I just did two tests, one 8 minutes, the >> other >> 4 minutes exposure. Both were highly overexposed (even a foam brush >> wont >> clear darkest part of the image). Will try 02:00, 01:00 and 0:30 >> exposures >> and then share the results... Coating is easy as long as you brush >> presistently for a long time (emulsion doesn't bead much) and you keep >> the >> emulsion very thin (if not, flaking occurs). >> >> One important problem is: the base gets stained (not pigment, some kind >> of >> chemical stain), and doesn't seem to clear with sodium metabisulfite. >> Will >> see how it goes with shorter exposures. If it continues to stay so then >> I >> won't be able to get pure white -> only ecru / warm background. Not a >> problem for some images, big one for others... >> >> The base coating consists of: >> 1 part acrylic gesso >> 1 part calcium carbonate powder >> 1/2 part water (all by weight) >> mixed homogenously giving a creamy consistency. Applied with a foam >> brush, >> smoothed gently with a watercolor wash brush. >> >> I must admit it's not much interesting for Yupo. But if I manage to >> make >> it work, it can be used as a nice way to print on rigid / impermeable >> and >> smooth substrates such as aluminum sheets or MDF, HDF or plywood... >> >> More later, >> Loris. >> >> >> 2 Kasım 2008, Pazar, 5:43 pm tarihinde, Marek Matusz yazmış: >>> >>> Erie, >>> If you look closely at the pictures that I posted you can see the >>> "imperfections" in the print, but these are best prints on Yupo that I >>> kept. Gelatin sizing was a total disaster with the gum layer not >>> sticking >>> to it at all. >>> >>> What worked best for me is no treatment to the sufrace at all. Very >>> thin >>> gum layer (means dilute gum solution) rolled with a gum roller gives >>> decent results. It seems that the thinner the gum the better the >>> results. >>> My exposures got very short as well, around 30 seconds. I wonder if >>> scrubbing the paper with cleaning powder would help a bit?
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