In this exercise, you will be creating a sphere, but the same principles apply whenever you’re drawing or painting any form in a representational artwork.

Use the diagram below, watch the accompanying video lesson and read my introduction to form as guide when you create your own sphere.

The Form Principle.jpg



  • Paper
  • Pencil or charcoal
  • Eraser


  • Toned canvas or panel
  • White paint
  • Either black paint or
  • An earth colour paint (such as burnt umber or raw umber)
  • 2-3 small to medium sized brushes
  • Odourless mineral spirits
  • Palette
  • Cup for mineral spirits
  • Cleaning rag



Determining the Light Source

1. Draw a circle on the page or canvas, this will be the basis for your sphere. Then draw an ellipse on the ground plane, this will be the shadow cast from the sphere and determine the direction of light.

2. Draw the ‘bedbug line’ (the line that divides light from shadow) onto the form.

Establishing the Shadow

1. Fill in the the shadow shape with an average shadow value (about a 7 on the value scale).

2. Next, fill in the cast shadow on the ground with a similar value.

Adding Variations to the Shadow

1. The shadow isn’t usually evenly dark, because in most cases, light will be reflected into the shadow after bouncing off other elements in the scene. This will cause the centre of the shadow to lighten, becoming darker towards the bedbug line (the ‘core shadow’).

2. The shadow will also become darker where two forms meet one another (like where the sphere meets the ground). This is called the ‘occlusion shadow’, it is dark because neither direct light or reflected light reaches it.

Adding Halftones and Refining the Form

1. Begin adding halftones from the bedbug line, these are the ‘dark halftones’. As the halftones move further away from the bedbug line they will receive more light, and begin to lighten as a consequence.

a)  If you are painting on a toned panel, at a certain point you will reach a value that matches the canvas. When this happens you should stop adding dark halftones and start working out from the lightest values. You will find these values at the part of the sphere that faces the light source. Once you’ve added all the lightest halftones, they will meet the darkest halftones.

  1. If you are drawing your sphere you can just keep adding halftones gradually. The further that halftones are from the bedbug line, the lighter they will be. At some point you will just leave the white of the paper.
  • In stronger, direct light, the transition from the bedbug line will be more harsh.
  • In weaker, diffuse light, the transition from the bedbug line will be more gradual and softer.

2. Now that all the halftones have been added you should have a roughly correct sphere. At this point you should spend time correcting value relationships and neatening up your painting or drawing.

As always, if you have any questions about this exercise, please let me know.