Visual arts are conventionally classified as spatial arts; they can be apprehended in a single moment. Yet, arguably, they also codify a temporal dimension which is elided by the spatial vs. temporal art dichotomy. Acrylic paints dry very rapidly, dry to a darker shade, and create layers of application that have a uniform level of saturation throughout a brushstroke. These facts about the medium compel the acrylic artist to constantly mix colours for each part of a painting, mix colours a smidgen lighter than they intend it to appear in the final work, and achieve any gradations in colour intensity implied by the lights and shadows on the subject using as many tints and shades of the local colour as may be required to achieve smooth transitions. By contrast watercolours dry relatively slowly, dry to a lighter tint, and create applications that have a gradated saturation going from high to low from the centre of a brushstroke to its peripheries [modulo the wetness of the paper].