|Paolo and Francesca da Rimini (1855) by Dante Gabriel Rossetti|
Watercolour has a life of its own. You make your mark on the page and very soon it's not entirely yours. The paint sinks into the surface, seeping, running, spreading disastrously or drying too fast, forming suggestive blots or stains. No matter how quick you are – or how slow – it does not stay put, or remain stable. The colour comes, and it goes, drying unpredictably by evaporation.
Too wet and watercolour will pool, buckling the page. Too dry and it will stop the brush in mid-flow. It reacts badly to a drop of rain or too much heat, to the artist's impatience or aggression. Although it accommodates happy accidents, it is also disaster-prone right to the last-minute mishap of the water jar farcically overturned.
It cannot be displayed in direct sunlight without fading like Tinkerbell. So it is to some extent a hidden art, preserved behind veils or between the covers of portfolios and albums, languishing under wraps in stately homes and museums. Everyone knows that watercolour gradually weakens. Indigo can age to brown or even pink. The brightest green may dwindle to grey.