Thread: Gesso problems
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Old 01-01-18, 04:13 PM
Koo Schadler's Avatar
Koo Schadler Koo Schadler is offline
Tempera Painter
 
Join Date: Dec 2003
Location: Alstead, NH & Zirahuen, Mexico
Posts: 316
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Hi Chris,

Excuse the tardy reply – you’ve probably been working away and have already figured out the answers to your questions!

Paints are essentially composed of three ingredients: binder, pigment (or filler), and vehicle (or solvent). A simple, not inaccurate way to think of traditional gesso is that it’s essentially a very high PVC paint. High PVC (pigment volume concentrate) means paint with a high ratio of “pigment” (in the case of gesso, an inert white filler) to binder (in the case of gesso, animal glue). High PVC paints make porous, absorbent surfaces. This is ideal for a tempera ground because (a) it allows the paint to mechanically bond and thus adhere, and (b) allows the painter to control the water content in the paint (the absorbent gesso underneath acts like a sort of sponge).

The “pigment” or filler in gesso should be:

1. Inert (i.e. you don’t want a chemical reaction to take place when water is added, such as when water is added to lime)

2. White and opaque (to increase the reflectivity of the ground so light bounces off, is not absorbed by it)

3. A proper crystalline structure to produce a hard, durable surface (versus, for example, talc, which makes too soft a surface.)

There are many chalks (calcium carbonate) and gypsums (calcium sulfate) that meet the above criteria. My preference is marble dust because I like the quality of surface it produces (but I suspect also because of the name itself: how seductive to paint on top of marble!) Other artists prefer gilder’s whiting, French Chalk, whatever you like best. I can’t think of a reason to make your own whiting.

Regarding thick paint: In my first reply to you I didn’t mean to imply that you can’t paint thickly in tempera. I was trying to address one reason why your flower petals may have come out looking “stiff and artificial”. As Rob notes, you certainly may apply tempera densely– in fact, I always start my paintings with thick paint (heavy cream consistency, which is about the thickest possible in tempera), then transition to increasingly thin paint on top of that, reverting to thick paint at the end for highlights (I don’t intend that as a description of how one should work in tempera, merely explaining my working method). As Rob says, the most important thing is to experiment, play, and build on your experience. Paint often, with attention, curiosity, and a wee bit of fearlessness.

There is a limit to how thick tempera paint can be applied without risk of cracking. I’ve let tempered paint sit on the palette to thicken to about the consistency of tubed oil paint, then tried applying this thickened tempera to test panels in impasto strokes, and hairline cracks appeared upon drying. I'm curious, Rob, how thick would you say your friend’s paint is? I’m always interested in people pushing the limits of ET. Please go visit him, so you can get a good meal at the same time.

Happy New Year to all,

Koo
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