Optical Effects - Transparency

For some time I've been reading instruction on properly handling egg tempera. Not the tempering--I think that's coming along mostly okay. It's the application of light over dark, dark over light, and same over same. I hope within the next few posts to gain a handle on these techniques.

For tonight, an introduction quoted from The Practice of Tempera Painting:

Basic principles of tempera painting

"In the application of the tempered color, it is necessary to understand and apply the optical principles which govern the behavior of colors in tempera. Regardless of the pigments it contains, no well-tempered mixture is absolutely opaque; and, as each mixture ordinarily contains some white, it is not absolutely transparent. Its opacity and transparency are relative, and are conditioned by the values over which the mixture is applied. If it lies over a lighter ground, it appears transparent. Light strikes the paint, passes through it, strikes the lighter ground, and is reflected back to the eye through the layer of paint. Some light has been lost in surface reflection, some has been absorbed in passing through the paint film in each direction, and some has been absorbed by the ground. But as long as the ground is lighter than the paint, it will reflect some light back through it, and produce an effect of transparency. Any color in tempera laid thinly over a lighter ground will act as a glaze."

Yellow ochers for bases painted over with Ultramarine Blue, Cobalt Blue, and Chromium Green. Hmm... perhaps I should have used only a light wash but a mix of overlays might help sort things out. Not sure yet where all this is going but I will step through the techniques, having faith that light will shine in on all this.


Thompson, Daniel V. Jr. The Practice of Tempera Painting. New York. Dover Publications. 1962. (Yale University Press. 1936.) pp. 100-101.