Let us recall our lesson on sunset and sunrise and remember the effect of atmosphere on light rays.
Remember how the motes in the sky or mist intercepted the long blue rays and let the red through?
Now we will treat that 'mist' as a piece of glass or plastic; a solid yet semi -transparent medium.
In the first example below the reddish pigment particles suspended in the glass are sparsely arranged.
As with the earth's atmosphere at sunset the pigment particles in the glass absorb the blue-green light rays ... and this has a dual effect. (Fig 1.)
1. It reflects the red light rays back to the observer making the glass appear red.
2. It allows some of the red rays through to strike the surface behind. Here, that surface (green), absorbs some of the red rays. This tends to slightly neutralize the color. If the green was stronger the shadow would become grey.
The solid object in Fig.2 blocks out all the light rays and casts a theoretical neutral shadow. Most painters find it useful to paint a warm shadow if the light source is cold and a bluish shadow of the source is warm. In this example the greenish background and reflected side light prevent an altogether neutral effect.
In the third example thicker glass is added to the center. This has the effect of both blocking the light and un-saturating the red. (see previous lesson on saturated color)
The principle regarding transparency is useful when painting with semi-transparent dark paint as the value and depth of the darks can be increased. As opposed to opaque darks, transparent dark allows light to penetrate the surface before reflecting back off what is underneath. This has the effect of filtering out light rays on the way in as well as on the way out thus allowing less of the light rays to escape and for our eyes to read richer, more ineresting darks.
THE SEMI-TRANSPARENT RED RUBY RING
1. Create an oval and smear with shades of red allowing a transparency around the edges. You could do this with a semi-transparent crimson red like alizarin.
The rest is pure fiction and applied logic ...
a) Light source (top left) determines the position of the shadow as well as the position of the reflected light on the stone.
b) The highlight on the stone tell us the much. As it is sharply focused we know the stone is smooth and shiny (very reflective). Here it is a window - reflected twice (the second time gives the stone greater transparency). By its position we also know the window is the main light source for the object and a line drawn from the observer to the highlight would reflect at an angle and pass out the window. This tells us that the object's surface is at an angle (round) and that the window is high left. This information should tally with the position of the shadow.
c) The horizontal bands on the ring band define its texture and roundness. The elliptical shadow reinforces this assumption.
Here again this object is not drawn from anything real. It is a pure construction using logic and remembered observation.
STUDENT ACTIVITY: Find examples of gold, silver, chrome and copper and describe them in terms of reflectiveness, edge and color (light hue and dark hue).