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Painting Rainbows

Rainbows are one of the most challenging landscape painting subjects.

Their colours are intense and (fairly) pure and additive. In contrast, paints are subtractive and the necessary mixtures all too easily slide into muds. Rainbows are ethereal, they do not really exist except in our minds yet the thick pigments needed to achieve their colour saturation easily transforms them into the rigid girder work of a railroad bridge rather than the delicate mind work of Bifrost, the rainbow bridging the Viking Worlds of Midgard and Asgard.

John Constable�s bow in his �Salisbury Cathedral� is an unbelievable solid and steely affair. Turner�s �Buttermere Lake� bow is moody and almost colourless in a dramatically dark landscape. Yet it feels like a rainbow, one that could well have resulted from small raindrops producing a broader and weaker coloured near fogbow.

Frederic Church of the Hudson River School got it right in his �Niagara� and to a lesser extent in �Niagara from the American side�. Both need viewing in the flesh to properly appreciate them. Stand up close enough to make the gallery attendant nervous and so that the bow really does have a radius of 42�. Church did less well in his �Rainy season in the tropics�: His colours are too thick, too banded and the secondary is narrower than the primary not to mention too close to it.

It is easy to criticise - try painting one! One secret, well shown above by Mark Rutkowski is to portray only a segment. Be brave - outdo Constable!
Light colours add.

Primaries mix to white

Tropical Cumulonimbus

Both photo and painting portray grouped towering cumulonimbus clouds, some with characteristic anvil tops.

The artist’s horizon is blackened by rain pouring from the cloud’s base. Rain obscures some distant hills in Franks image. If the images were videos the clouds might flicker with lightning.

Tropical cumulonimbus clouds are one of the drivers of global atmospheric circulation by transferring heat and moisture from the tropics. Intense ground heat warms low-level moist air causing it to bubble upwards in powerful updrafts, as it expands it cools and water droplets condense. Eventually the cloud top reaches equilibrium where high altitude winds form the anvil.

The top is some 12km high at the tropopause and some clouds actually punch through into the stratosphere. Individual cumulonimbus cells can organise into larger mesoscale convective systems.

Frank Nieuwenhuijs photographed this rainbow against a dramatic sky at Desa Wairterang on the�north coast of East Flores, Indonesia. Just a few days later he was browsing the Purpa Fine Art Gallery Seminyak on Bali. He was astonished by the painting at right by artist Mark Rutkowski. It could almost be a mirror image of the same spectacular scene. Enormous tropical cumulonimbus dominates both.

Paint colours are subtractive.

Primaries mix to black