The 23 year old Joseph Mallard Turner exhibited "Buttermere Lake, with a Part of Cromackwater, Cumberland, a shower" at the UK Royal Academy in 1798. He based it on a sketch made the previous summer while on an eight week several hundred mile tour of the North of England.
It is a dramatic, dark and stormy scene. Light of some sort spills fitfully on the village of Buttermere in middle distance while foreground Crummock water are surrounding crags are in inky shadow. A white bow bridges the scene. There is a trace of a secondary bow.
Turner is conjuring the Sublime - a view evoking awe and wonder at Nature.
What exactly is portrayed? A white fogbow? Is it a night scene with a ghostly moon bow? Or, if it is day and it is a rainbow, why is it white? Did turner observe the bow directly or did he add one in his London studio. If the latter, did he get it right?
The bow's shape, the landscape colour and lighting
The bow's height and almost semicircular shape tell us the sun (or moon) was low in the sky. Only about XXX degrees high as estimated from the bow’s height.
The picture looks to the SE XXXXX and, since all bows are opposite their light source, the latter must be low in the NW. Some fields and village of Buttermere are in fairly sharp orange light. The clouds have some characteristic Turner murky yellow-orange highlights with hints of red (?) on something like Prussian blue or ultramarine. This all indicates a near sunset scene. Not a nocturnal one with moonbow.
Fogbow or rainbow? Neither the painting nor the sketch have fog or mist. Distant hills are sharp and clear. The sky is stormy. Not fogbow conditions. The bow is also too narrow to be a fogbow. We are left with a rainbow. It extends in front of the distant hills indicating a nearby shower just as Turner says in the title. Effective as the white bow appears, where are the true colours?
Turner painted many rainbows although mostly in watercolour.
A few examples...
The Buttermere bow is not alone in being white. It is not entirely white. There occasional hints of red and blue especially at its top. At most most of Turner's bows have a faint red stripe on their outer edge and blue on their inner. .... A less effective exception.....
Rainbows are devilishly difficult things to portray in paintings. To merge the multiple hues well in their correct geometric positions is hard A further challenge is reproducing the bow's delicacy and transparency. There are very few natural bows so intense that you feel you could slide down them or safely cross Bifrost from Midgard to Valhalla. They are the exceptions. Most attempts to paint rainbows result in something that is just unreal and unconvincing, or garish. Did Constable really succeed with Salisbury Cathedral?
F E Church, a superb painter of the American Sublime, arguably failed with his Rainy season in the Tropics. Church himself put a white bow into his 1856 Niagara painting as did Bierstadt.
That Turner chose to portray rainbows largely without colour is no criticism of his ability. On the contrary, with his white bows he got it right. His almost symbolic renditions avoid garishness and solidity. He conveys their spirit, luminosity and ethereality - what more could we want?
Is the bow accurately placed?
Turner's 1797 sketch shows little or no sign of a bow. There might be a hint in the white patch at centre where the subsequent oil painting's bow nears the ground. The painting's bow was added in the London studio without (known) references to "on site" observations.
A sunset rainbow at his location has its extreme position at the summer solstice. The sun then sets at its furthest north and the bow's centre at its furthest south. This is to left in the painting. Bows at other dates are even further left.
The diagrams show the midsummer bow together with Turner's. A bow as he placed it is impossible. The 1797 sketch has some faint and tantalising streaks of red probably added later with the other coloration's at his Lake District lodgings. They almost suggest that Turner was playing with rainbow placement possibilities. Compositionally he chose wisely, a rainbow in the scientifically correct position just would not have worked.
The reflected bow
There is a bow reflection (technically a 'reflected bow' to the left of the lone boatman. Not to add insult, this is also incorrectly placed. Turner has placed his reflection more or less on a continuation of his rainbow's circle. That would only happen at exact sunset.
Turner's white bow could - on its own - be interpreted as a moonbow, fogbow or rainbow. A combination of factors show it to be a rainbow with the sun low in the western sky.
The white rather than coloured bow is a common Turner portrayal and better conveys a rainbow's luminosity, transparancy and ethereality. Other, later, painters of the Sublime did the same.
Turner took considerable liberties for compositional purposes with the bow placement. His position is impossible. Any bows visible at his sketching location would be on the painting's left.
The placement of the bow's reflection in the nearby water is erroneous.
All this is not to distract from a masterpiece.
I Buttermere Lake, with a Part of Cromackwater, Tate Gallery, London
J M W Turner, Buttermere Lake, with a Part of Cromackwater, Cumberland, a shower, 1798 Tate N00460, digital image © Tate released under Creative Commons CC-BY-NC-ND (3.0 Unported)
II Crummock Water, Looking towards Buttermere - From 1797 sketchbook, Tate
J M W Turner, Crummock Water, Looking towards Buttermere, 1797 Tate D01086, digital image © Tate released under Creative Commons CC-BY-NC-ND (3.0 Unported)
III Malham Cove with Cattle Grazing, The British Museum
J M W Turner, Malham Cove with Cattle Grazing, 1797 Tate 1910,0212.277, digital image ©The Trustees of the British Museum, released under Creative Commons CC-BY-NC-ND (3.0 Unported)
IV A Rainbow, with Cattle, Tate
J M W Turner, A Rainbow, with Cattle, c1815 Tate D17197, digital image © Tate released under Creative Commons CC-BY-NC-ND (3.0 Unported)
V Rainbow and Coastal Terrain, Tate
J M W Turner, Rainbow and Coastal Terrain, c18140-5 Tate D36302, digital image © Tate released under Creative Commons CC-BY-NC-ND (3.0 Unported)