The ‘koudai’ or footring must ‘fit’ with the body of the chawan, the ‘do’ or chawan body needs to work together. sometimes i see chawan with very shibui or rustic bodies and a wheel trimmed foot.
incongruous or not in harmony.
more importantly is the floor of the chawan
The main implement or chadogu for stirring is the chasen or whisk. The form of the chasen must also ‘fit’ or allow the user to whisk the matcha with full contact with the floor of the chawan with no ‘dead spots’.
below image. having a smooth inner floor or chadamari assists in preserving the chasen from getting battered. in addition having an interesting area for the matcha to pool after drinking is also part of the equation.
much like a glove fits the hand, the form of a ‘ergonomic’ chawan is a form that fits the hand like a glove when held. there is two way sensory dialogue between the fingers/hand and the psyche.
harmony of form which includes a koudai (foot), body (dou), chadamari (tea reflecting pool) and kuchizukuri (lip). as a maker, its ‘all of the above’ balance of harmony of the above which contributes to a chawan that ‘functions’.