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-   -   Help!! Too much glue in Gesso recipe (http://www.eggtempera.com/forum/showthread.php?t=1146)

tjatkings 25-07-17 03:26 AM

Too much glue in Gesso recipe
 
Hey All,

So happy to finally be able to post on this forum. I have been practicing with Tempera for several years and this site has proved to be an invaluable resource. Last I checked membership was closed so quite excited to be writing this finally.

I have a question related to gesso panels. Have been making gesso with Kama Pigment's extra refined rabbit skin glue and in general it has worked well. I decided to try my luck and modify the standard recipe a bit as I had wound up with hairline cracks all over some panels. I think this time I used too much glue - after seven coats of the glue the gesso has almost a gloss too it and is very hard. It is still sandable and I was able to get it relatively smooth but the gloss is still present. I am worried about the paint adhering to the panel - if the surface is too hard/smooth. Should I be worried about this or should I just go ahead? Anyone have experience with this?

Alternatively, I paint in is oil as well, so at the moment my plan is to throw an oil ground over top and use them for oils instead. It would be a shame, but I can always make more.

Look forward to speaking to you all. Cheers!

Tyson

RobM 25-07-17 04:22 PM

Hi Tyson, welcome to the forums.
I always stick rigidly to one recipe as outlined on the main web site. For well over 20 years I've never had a panel fail. Yes, my grounds have a hard and slight gloss and there has been no problem with any of the paintings. Suggest you try some egg tempera paint on a corner of the panel and see if it adheres. I see no reason why it should not.
Rob

Koo Schadler 26-07-17 01:11 PM

Hello Tyson,

Just to clarify...it is always this site's intention to welcome every legitimate voice to the conversation. The only reason membership is sometimes closed is to allow the folks who voluntarily maintain the site to deal with spammers, etc. Those same volunteers are currently working on updates to ensure the site's open format and future - but given that work is done gratis, amidst full time jobs, it can take a while to implement improvements. MANY THANKS to the talented people who keep the forum up and running, merely from generosity and a love for egg tempera.

Onto gesso. Rob is of course correct, the recipe on this website gives the ideal ratios for traditional gesso. Testing for adhesion is a good idea. Here are a few more thoughts (in my usual, long-winded way).

All paints are made of three things: BINDER (egg yolk or oil or gum arabic, etc) + SOLIDS (pigments) + THINNER (water or oil solvent, etc). Every paint has an ideal ratio of binder to solids. If a paint strays too far from an ideal ratio, problems of either poor adhesion (too little binder) or cracking (too much binder) can occur.

Gesso is essentially paint. It has a binder (glue) + solid (chalk or gypsum) + thinner (water). As Rob notes, the recipe on this website gives what are generally considered ideal ratios for gesso: 1 part glue : 16 parts water : 24 parts chalk or gypsum. This mix yields a gesso that is not too soft, not too hard, but (like Goldilocks' porridge) just right.

There is a wee bit of flexibility in the ratio of binder (glue) to solid (chalk/gypsum) in gesso. Using slightly less glue/more solid (i.e. 1 part glue : 18 parts solid) yields a softer, more absorbent gesso (the water in the paint sinks in more quickly on such a surface). Use sightly more glue (i.e. 1 part glue : 14 parts solid) and you get a harder, less absorbent gesso. It's personal preference - what working properties you are looking for in the surface and the paint. As long as you get good working properties (the paint doesn't slip or lift too readily) and adherence (the paint, once dry, isn't easily rubbed off) it's okay to slightly adjust the standard gesso recipe.

The problem is if you stray TOO far from the ideal ratios. My biggest concern with your panels is that the ratio of binder to solid has gone far enough outside usual parameters to cause hairline cracks. This doesn't bode well for it's future. The cracks are stable now because they aren't changing because animal glues don't polymerize or cure (unlike drying oils or egg yolk). But as moisture (both during the painting process and later via relative humidity) travels in and out of the panel, the binder will be impacted by that moisture and cracking may increase. So even if you test for adherence and it is good (which it probably will be), and even if, as you build paint layers, you don't run into problems of slipping or lifting (which can happen when tempera is applied to an overly hard, glossy surface) I would be concerned about cracking (in a day, a year? Who can say....) impacting the paint layers.

As Rob says, a hard surface and slight gloss are not the problem (the average gesso surface is slightly hard and glossy); however it can be a problem to have EXCESSIVE hardness and gloss, along with cracks.

Do you know specifically what ratios you used? If so, that might clarify things. After all, if you didn't stray too far from the ideal parameters, too much glue may not be the problem. Cracking also can be caused be bad or overheated glue.

But, to be frank, the most logical conclusion is that there is too much glue in the formulation. I applaud you for experimenting with gesso, trying something new, but I also know (firsthand) it's a drag when such experiments extract a price!

As for throwing an oil ground over the panels, my inclination is to say don't do it. Yes, the oil ground and oil paint layers would seal the front of the panel from moisture, but the back and sides can still absorb humidity and thus encourage the latent gesso cracks to grow. If you could be 100% certain of sealing all surfaces, so no relative humidity can enter in, maybe that would work, but seems a bit risky to build on a shaky foundation. Then again, I tend to be conservative in this regard.

Good luck and welcome to the forum,

Koo


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