"Calligraphy is a picture of the mind."
"Enso is the circle of infinity, symbol of simplicity with profundity, emptiness with fullness, the visible and invisible. It sometimes forms a moon, sometimes a rice cake.
Usually the circle is begun near the bottom of the left-hand side and the ink is thickest there. Although the shape is the simplest imaginable, each circle is different. Some are almost perfectly round and others are quite lopsided. The shading of the ink also greatly influences the effect of the character. In your practice it is good to write one enso each session."
~John Stevens, Sacred Calligraphy of the East, p. 190.
Here are some of my fude 筆 (brushes):