Re: Tacky attraction< (was Solarplate images...website)
I think using the krene, low pressure, and not waiting much time at all
between drawdown has helped me with the patches...but they're still
there if I'm not careful and am working large.
I like your spray fix idea for the OHP. A fine matte acrylic coat on
the image side might just work. That seems to be the least pain in the
butt, in any case... I'd try that with all the other steps in
place...and if it works, remove the baby powder step and see if it's
still needed. Continuing to work with an image with smooth grey tones
to accentuate the problem will help you determine when the problem has
been solved.
I'm going downstairs to burn a plate I've had "airing out" all night.
Will do the drawdown test and see if the patches start encroaching
before burning the plate. In the meantime, do let us know how your
coating idea works. Sounds like it may be the ticket...
Jon
SusanV wrote:
Jon,
My vacuum is at about 22 inches mercury. I can adjust that with my
bleeder valve, and did that yesterday to see what difference it made
(remembering your prior comments about this). The spots were clearly
evident, and larger (meaning the film was farther from the plate),
with less drawdown. I tried it at 5, then 10 and 15, etc... the
higher the number the smaller the spots.
Another thought ... what about spraying some sort of clear-coat on the
ohp inked surface to make it less tacky? Like artist's grade
fixative. I have plenty of that... I'll try it later. I would
imagine a workable fixative would be best, because it's less glossy
than a final fixative. A glossy (smooth) surface is not the goal.
Actually... a semigloss polyurethane (hardware store) spray might work
just as well.
Oh the heck with it... let's just outfit these injet printers to print
right on the surface of the plates! Yeah, that's the ticket.
susan
On 2/27/07, Jon Lybrook <jon@terabear.com> wrote:
Great ideas Susan. Question: How much pressure does your vacuum frame
generate? I assume there's a gage, and if so, is there a
pressure-release valve to reduce the pressure somewhat during
exposure? I have my pressure at about 12psi and don't allow it to
drawdown for more than a few seconds during the image exposure. This,
plus the baby powder seems to help mitigate, but hasn't solved the
problem entirely. More comments below.
SusanV wrote:
> So the leprositic measles we're getting in our gravure prints may be
> from the tackiness of the KM73 plate surface against the inked side of
> the OHP film. Talcum powder helped but didn't solve my problem. So
> now I wonder how we combat this tacky issue?
>
> We need to allow the trapped air to move to the outside edge of the
> plate/ohp sandwich, so the vacuum can pull it out.
>
> I'm just brainstorming here...
>
> corn starch (maybe it's better in some way than powders which have
> other additives)
It seemed a little too pasty between my fingers, so I was hesitant to
try it, but if nothing else works, it's worth a try.
>
> some wet type of lubricant? can't use water of course, but what about
> oil? would a light oil film dissolve the inkjet ink? Would it wash
> off the polymer plate easily during development? I could imagine
> using a brayer to bring the ohp in firm contact with the plate before
> exposing... working from the inside out to push air pockets to the
> edges.
This could theoretically work like mounting fluid does with drum
scanners, however I don't recommend it. With oil you'd have debris
clinging to it and the krene, and your vacuum frame would be a mess.
Oil or alcohol should be harmless to the plate, but alcohol would
certainly destroy the transparency and the oil, even if harmless to the
transparency might interfere with processing the plate...
>
> Using the brayer idea through Krene plastic during drawdown to help
> push the air bubbles to the edges of the plate where they could
> escape.
I believe I tried this once and didn't have any luck with it....but it's
the least invasive thing to try. Maybe try it before/during/after
drawdown and see if that is effective.
> one more thing... what if we expose the positive with the printed side
> UP away from the plate? Is the opposite side of the ohp as tacky?
> Would it make an unacceptable difference in image sharpness?
Yes, it would affect sharpness.
We also talked about a few other approaches, which I've tried but not
gotten conclusive results on (I was experimenting with too many things
at once!).
1. Remove the mylar from the plate the night before exposing it, and
leaving it out in a dark place to 'air out'.
2. Foot powder is supposedly 10x more absorbent than baby powder. I
tried it once (recently). It seemed to brush off the plate more cleanly
than the baby powder and wasn't as effective. Maybe try a combination
of baby powder and foot powder in conjunction with minimal drawdown time
and less pressure...
I'll be burning some plates this week and will try some of these things
too. I plan on trying the two approaches above and will let you know
how it goes.
Jon
>
> susan, frustrated.
>
>
>
>
> On 2/26/07, SusanV <susanvoss3@gmail.com> wrote:
>> Hi Jon and Chris and all,
>>
>> Update regarding measles:
>>
>> Today I was exposing an 8x8" plate (image exposure), and very clearly
>> saw the leprosy you describe during drawdown. I had dusted the plate
>> with powder but if that helped it didn't do enough.
>>
>> I removed the plate and positive from the vacuum bed, and tried
>> dusting powder on the emulsion side of the positive. It was
harder to
>> brush off and was leaving streaks, so I used a new microfiber cloth I
>> use in the darkroom, which worked well. BUT... the leprosy happened
>> again.
>>
>> My vacuum bed has a typical bumpy surface, but I have a smooth white
>> sheet of plastic over the center area. I noticed that the plastic
>> lifted up against the glass all around the plate and positive during
>> drawdown, and realized that using the plastic possibly circumvents
the
>> design of the pebbled surface, which must be to allow air to flow
>> through all those little channels between the bumps. So, I removed
>> the plastic and tried again. Initially got the same result, but then
>> let the drawdown continue for a minute or so, and it did seem to
>> improve.
>>
>> By the way... I tried different drawdown times, and the spots got
>> smaller with longer times.
>>
>> I eventually just let it draw down a couple of minutes, then made my
>> exposure, even though I could still see some spots. I've pulled 2
>> plates, and used paper that had soaked overnight, but still got some
>> small measles. The splotches are small and fairly regular and evenly
>> distributed, and mostly in the mid-tones. I'll scan it in the
morning
>> after it dries and post it to my blog.
>>
>> I'm still using the glass on my Nuarc... maybe tomorrow I'll build
the
>> frame for the krene plastic and switch to that. I was just impatient
>> today and wanted to print.
>>
>> Susan
>>
>>
>> On 2/20/07, Jon Lybrook <jon@terabear.com> wrote:
>>
>> "Susan: If you want to test this, take a virgin KM73 plate with the
>> mylar removed, and a virgin piece of OHP (without an image printed on
>> it), sandwich them under the vacuum frame and hit the switch on the
>> vacuum. I'll bet you see a similar, but subtle pattern of patches
>> manifesting like leprosy within the first minute of drawdown. The
>> aquatint screen, unlike your image transparency, is made of real film
>> and doesn't have this issue, but the OHP is tackier against the KM73
>> plate and this is the problem. The remedy for me has been baby
powder,
>> very lightly dusted over plate with a hake brush (Jan gave me the
idea
>> several years ago). If you were using baby powder, the other key
is to
>> not let the image exposure draw down too exceedingly long. I
basically
>> wait until the Krene goes flat against the bed, then hit the exposure
>> switch with no extra drawdown time beyond that. Since the screen
>> exposure is not the issue, you can draw down on it as long as you
want.
>>
>> --
>> susan
>> gravure blog at www.susanvossgravures.blogspot.com
>> website www.dalyvoss.com
>>
>
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