Re: Tacky attraction< (was Solarplate images...website)
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: 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.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) 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...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. 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.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. Yes, it would affect sharpness.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? 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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