IT IS not every day you get a private view of watercolours by one of the greats of British painting in the company of a couple of experts. Even more exciting, one of the experts has a fancy gizmo which is shining a light – literally – on Turner's watercolours to reveal all manner of hidden delights.

Graeme Gollan, senior conservator with the National Galleries of Scotland (NGS), is the man with the super-torch and a whole lifetime of experience in tending artworks behind him. He is shedding light on various marks made by Turner's hand as a team of technicians cracks on with hanging the 38 watercolours gifted over a century ago by Victorian art collector Henry Vaughan.

Vaughan (1809-1899) thought like a curator and knew all about conserving art works. His gift, made in 1900, stipulated these watercolours, which present a snapshot of the entire career of Turner, were to be exhibited to the public, “all at one time, free of charge, during the month of January”.

This special private view for The Herald finds Gollan, senior curator Charlotte Topsfield and myself, gathered around painting after painting, ooh-ing and ahh-ing while savouring the sheer bravado of Turner's approach to painting landscapes. Even 165 years after his death, his pioneering use of paint and materials catches you like a blast of January wind.

The watercolours range from Turner’s early topographical wash drawings, copied from works in the collection of his mentor, Dr Thomas Munro, through to his atmospheric sketches of the Highlands and continental Europe’s expansive vistas from the 1830s and 1840s.

In looking at these watercolours, painted over the course of half a century, it is possible to track the major developments in Turner's art in one fell swoop.

"Let's see if we can find the thumbprint," says Graeme, as we lean into a late watercolour called Venice from the Laguna. It takes us a but of time but eventually we spot it. "It's there in the cloud of steam rising from the steamer!" exclaims Charlotte.

And so it is. Painted in watercolour, gouache and pen and ink during the artist's last trip to Venice in 1840, it's a dramatic painting, full of movement and still singing with colour. The city is silhouetted with the finest of lines on the horizon, on the verge of being swallowed up by a violent storm. Two clusters of wooden piles, marking channels across the lagoon, are on the right hand side of the roughest of seas, while a steamer careers off into the left hand side of the picture.

We move on to another work, The Piazzetta, Venice, painted during the same visit, when Turner was 65 years old.

Graeme flicks his torch onto a bolt of lightening crackling over San Marco, the much-visited square at the heart of Venice, which looks as if it is contained within the Piazzetta, the adjacent political and ceremonial heart of the ancient Italian city.

"We don't know for sure if this scraping mark was made by Turner's own thumb or with a scalpel," he explains. "But scraping is very much a Turner trademark. He used his thumb like a claw.” We pause to imagine Turner in mid-creation, scraping away with a giant paint-encrusted thumbnail like an eagle's claw.

When Turner was finding his way as an artist at the end of the eighteenth century, the art of watercolour painting was considered as cutting-edge as the most out-there Turner Prize-style contemporary art in the current art market. It is no accident that the often contentious annual contemporary art prize has been named after him.

Rapid technical developments in materials meant that Turner was constantly experimenting with new paint and surfaces. This has a knock-on effect for twenty first century conservators like Graeme, who has been with the NGS for 35 years. He is the one charged with the task of giving the Edinburgh Turners an annual health check.

"All the watercolours are mounted on pure cotton board which will never discolour," he explains. "Acid is the enemy of paper and these works are very well-protected. The glazing is also filtered so they have an extra layer of protection. They are very low maintenance as they are kept in perfect conditions of light and temperature.

"Turner understood materials very well and he tried everything in order to find out what would last. By the middle of the nineteenth century people were starting to realise watercolours were fading. Vaughan knew all about this and anticipated the further effects of light and age.

“We know blues fade. Skies and shadows go first in watercolours but these were received in the Gallery back in 1900 in good condition. There is evidence to say Vaughan kept them in portfolios."

In addition to the Vaughan Turners, the atmospheric exhibition watercolour Mount Snowdon, Afterglow, painted around 1800, has been drawn from the Gallery’s permanent collection and is also on display for the next four weeks.

Outside January, the 38 permanently-framed works are housed in a slotted wooden cabinet in the Gallery's Prints and Study Drawing Room. Since 1973, one visitor per day is usually allowed to view on appointment on a year-round basis. Because of the on-going construction of the new Scottish National Gallery Project and the reconfiguring of the gallery's libraries and print rooms, at the end of January, the bequest will be locked away for a few months until the new rooms open up.

Until them, you have 31 days to go and catch these sublime Turner watercolours as the low midwinter light of Edinburgh keeps Turner’s fleeting skies and shadows firmly in check.

Turner in January 2017: The Vaughan Bequest, Scottish National Gallery, The Mound, Edinburgh, from tomorrow until January 31, 2017. Admission is free

www.nationalgalleries.org