Memory is a very curious thing. I had a vivid recollection of spotting this picture at sale, and realising at once that it must be an early Gainsborough. For five minutes I might have thought it was by Hayman, and then the wheels started to turn, the penny dropped and quick as thought I knew it was by Gainsborough.

So it was a surprise last weekend when Dad reminded me that in fact he had called it first, and – the emails prove it – by one and half hours (which doesn’t count the time I’d already spent thinking about Hayman before he saw it).

I was intensely pleased. Dad has wanted to find a Gainsborough for a long time and he has always believed in this one.

(c) Matthew Hollow 2016. Courtesy of the Paul Mellon Centre for Studies in British Art

The sitter is unidentified, but it has been dated to c.1742 which makes it Gainsborough’s earliest known commissioned portrait, painted when he was about 15. I’m assuming that it must be a commission. The pose is too formal to be one of his family – I would think – and the dress is a real showstopper so I would say the lady must be a client being painted in her best.

This is a period of Gainsborough’s career we don’t know much about. He came to London from Suffolk in 1740 at the age of 13, when he painted one of the most remarkable self-portraits in art (Private Collection, formerly with Philip Mould). There’s a beautifully sketchy landscape that could be as early as 1741 (Christie’s New York 2003), and three pencil portraits from 1743/4 (National Gallery of Ireland; and Philip Serell Auctions). But before this portrait was rediscovered there were no known examples of oil portraits earlier than the portrait of a brother and sister of 1744 (Gainsborough’s House: a fragmentary portrait long divided in two, the brother’s portrait attributed to Hogarth and the sister’s lost; they were reunited two decades ago when Philip Mould rediscovered the sister’s portrait).

As soon as he came to London, Gainsborough threw himself into the art scene centred on St Martin’s Lane. His biggest influences and collaborators were Francis Hayman and Hubert Francois Gravelot. They both painted in the ultra-modern French rococo style, which blended portrait sitters with landscape backgrounds in a sort of elegant casualness. Gainsborough’s work in the mid-40s is painted in the same style. But Gainsborough’s early landscapes, and the brushwork in a portrait like this, show that he wasn’t simply influenced by Hayman and Gravelot; rather they encouraged him to paint as he’d always wanted.

The only thing we know for certain about the teenage Gainsborough’s earliest years in London, right at the beginning of the decade, is that he tried to make a career of portrait painting, but without great success. This portrait suggests that in the process, he would’ve had to try painting in a far more conservative idiom. The rococo was fashionable with the Prince of Wales and new-money, but the country gentry still preferred the way that painters such as Arthur Devis saw them. This small full-length portrait was painted by Arthur Devis at around the same date.

Arthur Devis Portrait of a lady c.1740 – 41 (c) Victoria and Albert Museum . Wikimedia commons

Gainsborough’s lady in a green dress is his response to portraiture such as this, and to patrons who must have expected it. At first glance, the lady in a green dress seems far more formal than the relaxed air of his portraits later in the decade. He uses the same etiquette manual pose as Devis, but the impact of the two portraits is so different. If I were writing about a contemporary young painter now, I would be tempted to use that handy cliche: ‘he takes the established idiom and subverts it.’ More accurately, you can see how he turns a conventional pose into a unique advertisement of his own style and talents.

Compare the correct folds of Devis’s silk dress with the casual fireworks of our lady’s green dress. That rough impasto on the sleeve is the same way Gainsborough shows the light catching the ruts of a cart-track. The hatching dark green shading down the side of her bodice is the same stroke you see in his trees. Someone once said that Gainsborough painted people as landscape. That was about the National Gallery’s Morning Walk, which was painted almost half a century later. You can see in this portrait that these lively, organic elements of Gainsborough’s style were present right from the beginning.

The face in the Gainsborough is a stroke of genius. Devis’s sitters are often cheerful, but they always wear a social mask. He can certainly suggest the expression behind the mask, but that is equally inscrutable. Everyone is always on duty.

The Gainsborough lady’s face – as I realised looking at it lit from the side – is built up from a mass  of light flickering strokes. Gainsborough’s technique of making a likeness from a flurry of impressionistic, random-seeming strokes more was a talking point later in his career. It’s exciting to see this taking shape so early. And it brings to life the unstillness of people’s real expressions. Gainsborough is able to give us a real person, and a real personality. There’s a challenging intelligence to her look, a real sense of wit and inner life, and you get the feeling this someone Gainsborough really enjoyed painting. And thanks to this Gainsborough scores the goal of portraiture – creating a ‘speaking likeness,’ as if it captures the briefest pause in a conversation.

Certainly he pulled out all the stops, and it’s a real showcase of is talents. Your eye is in constant movement round the picture, just as contemporaries said about Gainsborough’s later portraits, a nervous energy summed up by the firefly gold highlights round her head and down the front of her dress. The whole painting is like the visual equivalent of music. Gainsborough was a keen social violinist, and the feeling you get from this portrait is like hearing him jamming variations on a theme with his friends, music in light rather than sound. A great painter conjures the substance of objects by the way light works and moves across them, and in the flesh this portrait seems to glow.

When Hugh Belsey very kindly gave his opinion on the painting, he noted the mink-like sheen of the background, the beautiful, typically Gainsborough dancing line of the cuffs and the treatment of the gloves, which even suggests the fingernails. He also spotted a pentiment in the neck that we hadn’t seen. Gainsborough had originally shown her wearing a necklace, and then painted it out again. It was an inspired decision, and the pure, dramatic note of the lady’s bare neck is a key element in its beauty.

The portrait will be in Hugh Belsey’s catalogue of Gainsborough’s portraits, published by Yale next year, which is very exciting.