Something that skilled painters excel at is designing with value. What this means is that you don't paint objects or things. You see the shapes of light and shadow that these 'things' are made up of, and paint those.
The skillful part comes in knowing where to push values, making some slightly darker or lighter than they actually are, in order to link shapes. This creates a pattern of light and shadow that forms a strong design - the structure of your painting - and when done well, everything else that is built upon it will hold together in a powerful way.
The challenge for this simple exercise is to create your value study with only 4 values (+ white for highlights). By limiting values you are forced to designate the same values to some shapes that are in reality different in value. Shapes will naturally connect into an interesting pattern as a result.
Things to Keep in Mind As You Proceed
- Determine the important big shapes that fill the painting surface. Remember the shapes of the shadows and background are AS important as the shapes of the objects themselves.
- Draw out these shapes, filling the canvas.
- Block the shapes in with paint using only 4 values.
- Begin modelling form by introducing intermediate values within the shapes.
- Refine edges - hard and soft edges can be determined by squinting down. If an edge disappears when squinting - make it soft. High contrast areas will often be harder edged. Use your powers of observation to lead you.
- Finish with highlights and accents (small lights and darks) to complete the story.
Since I paint these studies alla prima with impasto passages, I don't then paint a color version on top. If you want to follow with color in a grisaille fashion, you could either paint your value study very thinly and wait for it to dry, or paint it in acrylic (as long as your canvas isn't oil primed) followed by oil on top.
If I want to do an actual finished painting, I will start a new painting using the value study as reference for the underlying structure I want to stay true to. If the colour or detail start to make things busy and the structure gets lost, I have the value study to lead me back to a sound design.