A value scale is a simple tool that identifies the relative darkness or lightness of a shape .
It takes about 15 minutes to make one.
Making a Watercolor Value Scale
Use just one color that will get thoroughly dark.
Leave a white strip at one end and paint the rest of the paper very light (2).
Dry thoroughly between layers.
Leave a strip of number 2 next to the white and paint the rest medium light (3).
Keep leaving a strip of the previous layer and darkening the rest till you have 10 patches with white on one end and black on the other.
Try to make uniform value jumps with each layer, but don't worry if it's not perfect. It will still work.
You don't need the numbers on your scale.
It's also not necessary to save a white border around your strips. Let the tones continue right off the edge of the paper.
Set up a shelf or a table where you can have a single light source. Lay out a sheet of monochrome paper or fabric on the table. Use a solid color, not a pattern.
Put a simple shaped object, like a piece of fruit or a mug, on the colored paper or fabric and turn on the light. Move the object around until you can see its cast shadow. Paint a simple version of the tableau. Patches of color would be fine.
Now replace the colored paper with a different color sheet, and look for the cast shadow. Paint this new tableau. Do as many as you like.
How is the cast shadow different rom the illuminated sheet of color?
We know the shaded area is darker. How else is it different?