Re: gum prints on Yupo

[Keith Gerling <keith.gerling@gmail.com>]

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?
>
>