There was no holding Arthur Melville back. An apprentice grocer in East Lothian in the 1860s who gave up his job to study art, he went on to become one of the great artist-adventurers of the Victorian age, and the most radical Scottish artist of his generation.

Perhaps because, at first glance, his works look traditional, as does his choice of medium (watercolour), Melville’s achievements are somewhat under-celebrated today. A major exhibition of his work at the Scottish National Gallery this autumn, the first for 35 years, aims to put the record straight. Curator Charlotte Topsfield says, simply: 'Prepare to be surprised.'

Melville studied in Paris and loved Spain, where he painted many important works, but he didn’t stop there. In the early 1880s, he travelled to Cairo, Karachi, through the Gulf of Persia to Baghdad, then overland to Constantinople. 'He was a very intrepid traveller,' says Topsfield. 'He really went off the beaten track. He was attacked by robbers in the desert and left for dead – it’s the stuff of adventures.'

Melville’s travels inspired him to invent new techniques in watercolour, painting with gouache on to wet paper to capture intensity of colour (the Spanish ocean in The Sapphire Sea glows like stained-glass) and the brightness of the Middle Eastern sun. 'He wanted to represent accurately that intense light,' said Topsfield. 'I think that’s what he was really interested in.'

Melville’s radical approach attracted criticism from traditionalists during his lifetime, though he was influential on the contemporary artists of his day, including the Glasgow Boys. 'Some of his landscapes are very abstract,' says Topsfield. 'A painting like The Chalk Cutting is almost all tonal creams and whites, it’s as if he is seeing landscape in terms of abstract blocks. It looks like it should have been painted by someone in the next generation, not by someone born in 1855.' (Susan Mansfield)

Scottish National Gallery, Sat 10 Oct 2015–Sun 17 Jan 2016, £9 (£7).