The value scale:
White is our lightest local color. A white bed sheet is lighter in value than a yellow sheet. An orange sheet would be darker yet, but still lighter than a black sheet. In typical indoor lighting, white is painted at value 10 in the light and 4 in the shadow. Black is our darkest local color. It is painted at value 4 in the light and 0 in the shadow. All other colors in the light will remain above 4, since they are locally lighter than black. All other colors in the shadow will be darker than 4 since they are locally darker than white. The halftones fall between values 7 & 2. Spend some time and thought considering this concept of value scale, it's role is crucial in representational painting.
Locals:
It is important to understand the idea of locals. It is the local quality of a white shirt that it is lighter than a gray tie. And a gray tie is lighter than a black vest. And they should appear that way under any lighting condition. A white shirt (a local of 10) is painted 10 in the light, has a halftone of 7, and is painted 4 in the shadow. A middle value gray tie (whose local is 5) will be painted value 7 in the light, 4.5 in the halftone, it's shadow at 2. It follows that the black vest (a local of 0) is then 4, 2 and 0 respectively.
Locals:
It is important to understand the idea of locals. It is the local quality of a white shirt that it is lighter than a gray tie. And a gray tie is lighter than a black vest. And they should appear that way under any lighting condition. A white shirt (a local of 10) is painted 10 in the light, has a halftone of 7, and is painted 4 in the shadow. A middle value gray tie (whose local is 5) will be painted value 7 in the light, 4.5 in the halftone, it's shadow at 2. It follows that the black vest (a local of 0) is then 4, 2 and 0 respectively.
Halftone Factors:
Surface texture: a mat surface catches and diffuses the light. A nap surface with many tiny bumps creates even more halftone. A shiny surface, with no texture to capture light, has no halftone.
Light level: A strong light creates less halftone, a weak light creates more.
Light source: a point source (light bulb, sun, photoflash) creates less halftone. A diffuse light source (north light, overcast day) creates more.
Form: Round, soft forms have more halftone. Hard, bony forms have less.
Brushing:
As a rule of thumb, it is good to keep the halftone narrow, since a wide halftone can ruin the form. If the halftone is narrow you can brush for it, meaning you can take a brush, zig-zag it through the adjacent light and shadow stokes, and brush back over the the zig-zag (see above). If this deadens the chroma, you may have to restate the halftone with more chroma and repeat.
Figure Painting:
Squint down at the halftone and determine if it masses with the shadow or with the light. Using Reilly's indoor palette, if the shadow is painted in at value 3, then the halftone will be painted at value 4 if it masses with the shadow, and at 5 if it masses with the light.
© John Ennis 2010
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