Georges Seurat's once-mocked painting Bathers at Asnières is both an "exquisite distillation of the very essence of summer" and "a modern wonder in the art of seeing".

The greatest works of art see seeing differently. From Jan van Eyck's The Arnolfini Portrait, 1434, with its bulbous fish-eye looking glass bolted to the back of the bedroom, warping reality, to Édouard Manet's A Bar at the Folies-Bergère, 1882, and its riddling ricochet of stares, these paintings play with our perspective and offer flashes of the world in all its strangeness. Some paintings perform their magic more stealthily, of course, without a mirror in sight. Take Georges Seurat's seemingly straightforward exaltation of summer, Bathers at Asnières, 1884 – a painting that, on closer inspection, peels away at our perception of perception with a passion and intensity that makes it as urgent and relevant today as it ever was.

At first glance, Seurat's colossal 2m x 3m (79in x 118in) canvas – much larger than gallery-goers were accustomed to encountering – is an outsized celebration of the lazy luminosity of the season, enshrining the relaxed mood of workers on a break from nearby factories as they bathe in etherealising sunshine along the banks of the Seine, northwest of central Paris. The light that polishes the pallid skin of figures who have spent too long stewing in the sooty fug of sunless foundries (those "dark Satanic mills" of which William Blake once wrote) seems initially to bestow on them a monumentality rarely seen in contemporary art and a grandeur typically reserved for the depiction of myth and history. Look closer, however, and their smooth and deceptively solid physiques suddenly begin to unstitch themselves, unweaving into a loosening mesh of pulsing photons – waves of pure hue and pigment distinct from form. The workers are animated in their motionlessness: hefty and weightless in equal measure.

In Seurat's hands, the very property of light, that most fundamental element that makes perception possible, is no longer a straightforward source of illumination. It is a substance that can, and must, be pulled apart and put back together again. Far from a simple celebration of summer indolence or the unwinding of mind and muscle against a tapestry of afternoon heat and haze, Bathers at Asnières is a deft dissection of the mirage of superficial appearances – an elaborate exercise in the undoing of the social and psychological veils that shroud our seeing and shape our world. It is a painting that sees into the life of things.

To unlock the latent layers of meaning in the work one needs a key and an expert guide. Fortunately, Seurat has provided us with both, hiding in plain sight, signalling our attention from near the very centre of the painting. There, just above the slumped shoulders of the central-most shirtless figure, fitted with a helmet of flattened auburn hat hair, is a slender chimney chugging smoke – one of several smokestacks that puncture the humid sky – that simultaneously interrupts Seurat's vision and is arguably responsible for every aspect of it.

The chimney rises from one of the many factories in the nearby neighbourhood of Clichy, the centre of French candle manufacturing at the time – an extraordinarily lucrative industry made possible by the scientific ingenuity of Michel Eugène Chevreul, a pioneering French chemist whose intellectual insights helped shape the 19th Century. In addition to isolating stearic acid – a crucial component of animal fat from which an odourless and clean-burning candle could be crafted – Chevreul is credited with formulating a........

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