Have a holy horror of useless impasto, which gets sticky and dull, turns
blue and heavy. When you have painted a bit of which you are doubtful,
wait till the moment when it will be possible for you to take it out.
Judge it; and if it is condemned, remove it firmly with your
palette-knife, without rubbing by rags which spoil the limpidity of the
pigment. You will have left a delicate foundation, to which you can
return and finish with little labour, because your canvas will have
received a first coating. Loading and massing the pigment is an
abomination. In twenty-four hours gold turns to lead.
_Puvis de Chavannes._