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  #21  
Old 21-01-05, 11:04 PM
turlogh turlogh is offline
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Default Re: glue gesso

Quote:
Originally Posted by Bert Congdon
Hello? Is anyone listening? :-?
Listening to what, exactly? You didn't ask any questions or solicit any comments.

I am always interested in another artist's methods and how he came to them. There are other good ways to work with hide glue and gesso. For example, I put the glue in warm tap water and stir for a few minutes. No sticking. I'm sure both methods are fine.
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  #22  
Old 22-01-05, 06:26 AM
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DLH DLH is offline
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Dear Joseph,

Iím shocked and chagrined. I made test panels and itís and it's an understatement to say that Iím surprised with the results. Iím sorry that I canít give exact recipes. I should have made precise measurements, but the following should be a good starting point anyone who wishes to experiment.

I began with the premise that much of the special absorbent character of traditional gesso grounds is due to the high stone to glue ratio. A kilo of finished dry gesso probably contains only gram or two of glue. Once dry the spaces between the stone particles are mostly air. Another characteristic of traditional gesso is friability. This means that when stressed it breaks rather than bends. This allows it to be sanded cleanly without clogging the sandpaper. If you have ever tried to sand over-bound gesso you quickly realize that friability is due to the stone/glue ratio, and not to any special property of RSG. At first thought this seems wrong. After all RSG can be crushed into powder. However, sanding generates heat that slightly softens the glue, causing it to gum up. (Tip: To salvage an over-bound panel, change your sandpaper often. Sharp sand paper generates less heat than does dull.)

I made PVA gesso by mixing about 10 cc. of white glue, (Elmerís Glue-All,) with 100 cc. water. To this I added 300 cc. of marble dust. As I mixed it I added water until it attained the consistency of heavy cream. I also made a similar mixture, substituting acrylic (Utrecht Acrylic Medium,) for the white glue. I applied three coats of each to a panel. I allowed each coat to lose its shine before applying the next. They both behaved very much like traditional gesso, except they didnít jell when they hit the cool panel. The acrylic was thixotropic, brush marks stood up until they were smoothed over. The PVA mixture, however, had remarkable self-leveling properties. To the remaining mixtures I added another 10 cc of PVA or acrylic, making the mixtures about two and a half times stronger. I applied these similarly to another panel. The stronger solutions required twice as much time to dry between coats. The stronger PVA was an even better self-leveler. Eight hours later they were all dry enough to sand. There were no cracks. They all sanded beautifully, the stronger gesso requiring longer sanding with sharper paper. No sample clogged the paper. Surprisingly, the sandpaper held up better than with traditional gesso. I made several shades of ET with mixtures of titanium white and spinel black. I could detect no difference in the handling and look of the paint on these new surfaces. The weaker panels were totally absorbent, while the stronger were slightly less so, but still well within the range of traditional gesso. All the surfaces took gold and silverpoint well. I could press harder, without the point digging in, as often happens to me with my traditional panels. I sawed through the panels and measured the gesso thickness. The acrylic gesso measured 1.5 mm. and the PVA almost 2. Using a highly subjective thumbnail test I crushed the edges to see how hard the gesso is. The strong PVA proved to be the hardest, followed by the weaker PVA, next in hardness was the weak acrylic, surprisingly, the strong acrylic made the softest gesso. None of the samples are as hard as traditional gesso, but I donít see this to be a problem, the PVA at least, seems plenty tough enough for our purposes. Its relative softness may be an asset. Traditional gesso is brittle. I have a painting with cracks caused by a blow to the edge. PVA gesso may also be more flexible, if so, it may be better able to withstand seasonal movement of the support.

The only potential problem with the PVA gesso relates to bubble control. Every gesso I have prepared contains bubbles. Some probably come from mixing, but I believe many come from air in the stone dust. Others in this forum have related their techniques for controlling these bubbles. I deair my gesso with a vacuum chamber. This causes the tiny bubbles to become huge and burst. The gesso boils energetically for minutes. Anyway, The bubbles in the PVA gesso showed more resistance to bursting than those in traditional gesso. I had to help the process along by shaking the chamber. This probably indicates greater surface tension. Another way I get bubbles is when I wait too long between coats. As gesso dries, water is displaced by air. This air bubbles up when displaced by water from the new coat. With traditional gesso, careful timing controls this problem. However, PVA generated a few, even with minimal drying between coats. The good news is that by rubbing each coat with my finger the bubbles were eliminated, and because the gesso doesnít jell, it remains receptive to this technique much longer than does traditional gesso, and, probably due to surface tension, the film self-levels even after manipulation.

Iím amazed. PVA looks, walks and quacks. I cant speak for Gamblinís PVA. Since it is sold as size I would think itís less concentrated than Elmerís Glue-All. The best guideline would be to start with a weak solution, then paint ET on the resultant panel. Keep increasing the ratio of PVA until the new panels show some resistance to paint absorption. From this point keep this recipe or go slightly weaker or stronger, depending on your taste.

Obviously, I have no axe to grind. More likely I have a petard upon which to be hoist. I apologize to you, Joseph, for ranting rather than responding to your sincere inquiry.

Good Luck,
Doug
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  #23  
Old 15-11-05, 10:21 PM
odyssic
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As an oil painter on linen, I definitely prefer RSG to PVA for a few reasons. One is the fact that RSG tightens the canvas whereas PVA seems to losen it. Another is the fact that RSG can be lifted off of the original support and remounted onto a new support when the linen (or whatever) begins to deteriorate. You don't have this backup plan with PVA available.

The key for longevity with oil is not to overheat the glue and to apply it as thinly as possible, just so it saturates the fibers and doesn't form a skin.

Also, I'm not sure what asthmatic reactions you have to RSG, but the fresher and higher quality it is, the less it smells. I've used samples that had almost no odor at all.

Also, I've tried a traditional gesso oil emulsion recipe for canvas once. I couldn't quite get it to work but it had potential, and could be sanded perfectly smooth for tempera use on canvas. It doesn't have much flexibility and yellows slightly due to the oil, but it was interesting and I'll probably try it again someday.

Steven
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