Crivelli’s St. Francis Receiving the Stigmata: Renaissance paint layers

What we see here is the European Poplar panel that has been planed and scraped into the general shape of the Crivelli panel. Wood is not evenly absorptive across the surface. So what we do is apply a layer of size, which evens out the absorption, and makes it more receptive to additional layers. What we use, and what was used for the most part for sizing throughout much of Western painting, is animal skin glue. So collagen that’s extracted from animal skin or animal bone. In this instance, we boiled up parchment scraps which were served as the source of that collagen.

What we’re looking at here is the panel but after the ground layers have been applied. So the panel, even when it’s sized, it’s not a very good surface for egg tempera painting. Egg tempera is a very translucent medium, it generally requires a beautifully, perfectly smooth white surface. And so what was done in the Renaissance is to apply multiple layers of what we call gesso, which is that same animal skin glue, but with a white inert filler in it, generally gypsum, that’s applied in many layers and then scraped to be smooth and receptive for the egg tempera paint. So there was no sandpaper in the Renaissance, if you wanted to smooth a layer of gesso—or many other surfaces—you would have to scrape it with a flat, metal, blade. So what was often done for panels is to rub charcoal over that white gesso surface and then scrape it until you don’t see any charcoal any more. At that point where you don’t see charcoal, it’s generally quite smooth. For this panel you see that there’s actually, there’s quite a bit of relief on here. So what had to be done is to create shaped scrapers for specific surfaces. So you see on here, the molding, had a specific shaped scraper so that it scraped it into that exact confirmation.

So what we see here is the underdrawing of the Crivelli panel. It was very very standard in the early Renaissance to work out your composition, often with charcoal or something like that. The underdrawing then was usually made permanent by the application of black ink, either with a brush or with a quill. This is most important on this Crivelli panel because much of this underdrawing is going to show through the paint layers and provide a lot of the modeling that we see in the final imagery. So gold leaf is very very important in early Renaissance Italian paintings. With water gilding though, it’s really almost impossible to gold leaf right up to an edge. So what was generally done is the periphery of the areas to be painted were scored with a sharpened metal stylus so that you could see that through the gold leaf, which would then kind of slightly cover that edge.

So what we’re seeing here is the application of red bole, which is a red clay in animal glue. This serves a number of purposes. One is, gold leaf is really not completely opaque. So what’s underneath it will influence the appearance of the gold leaf. The Middle Ages and the early Renaissance really loved warmer gold colors. So the red of the bole imparted a slightly reddish hue to the gold. Probably more important is, in gilding, any imperfections in the lower layers will show through and be magnified through the gold leaf. So it’s very important to have everything as perfect as possible before the application of the gold. A traditional technique is to use something slightly abrasive like a piece of cloth made out of horsehair, which can then allow you to polish that bole to a high sheen. So what we call burnished gold is really burnishing what’s underneath the gold.

What you see here is the panel after the gold leaf has been applied. Gold, as we all remember from grade school, is the most malleable and ductile of metals. Meaning that you can really pound it out into very large pieces and very thin. So gold coins would be pounded out, cut into multiple pieces, and then pounded again and again until it was at the final intended thickness. In water gilding, which is the technique for gilding of this era, or one of the techniques, the water activates the glue in the bole and then you float a piece of gold leaf on that water. The water’s drawn into the panel and eventually the gold leaf is drawn flat. There’s a window of time after the application of gold leaf where there’s enough moisture in the panel that you can take a dull punch and then punch into the gold and it will actually deform  the ground and the bole underneath. This worked to allow for light to be scattered. Remember, in a chapel, you would have candlelight and that would be playing across the gold surface. That punch work would break up the light and really allow for scintillating effects.

The primary medium in Renaissance—early Renaissance Italian panel paintings—is egg tempera: its pigments bound in egg yolk. What we’re looking at here is the first layer of egg tempera paint applied to the panel. You can see the underdrawing through this layer of egg tempera paint. Crivelli will actually use much of that underdrawing to model the final effects. Carlos Crivelli’s technique on this panel is very abbreviated: really it’s this base color, kind of a yellowish orange color. Then he added another layer of slightly more opaque, slightly redder orange to everything except for the skin. And then, hatched some shadows and highlights and that’s really most of what he used to create the modeling for St. Francis Receiving the Stigmata.