Some years ago, I bought a small head of Shakespeare painted on a rectangular fragment of canvas. It was like a miniature version of the Droeshout engraving, very dirty and ripe for the wildest speculation. My first thought from the auction catalogue was that it was part of a group portrait – The Lord Admiral’s Men! Perhaps even an early copy of the lost portrait that must be the source of the famous engraving.

Well, it was neither. It is a small Eighteenth Century memorial portrait, a few inches high, cut from its strainer and wedged in the frame against a piece of glass. Our restorer agreed with me that it could date as early as the 1740s, and this set off another train of thought. – Was there something distinctive in the pigment? the handling? What if this was painted by the young Gainsborough, back when he first knew the David Garrick in the early ’40s?

When it comes to your own paintings, putting Reason on hold like this can be irresistible. It is Schroedinger’s Gainsborough, simultaneously by and not by him, never to be put to the ultimate test and free to tumble through the airy realms of ‘What if?’

Right now it is next to be cleaned. I will post an image of it when it’s ready. Large, if it is convincing, and small and pixellated in the background if it isn’t. I don’t mind either way because it’s a picture that Zak and I love.

But Dad reminded me that Gainsborough did paint a portrait of Shakespeare. He describes it to Garrick in a letter of 1768.

The Letters of Thomas Gainsborough by John Hayes 2001. (‘D–k’ is Samuel Derrick (1724 – 1769), drunken poet, hack writer and later Master of Ceremonies at Bath, who compiled an annual directory of London prostitutes.)

Gainsborough’s problem with the existing portraits of Shakespeare, the Chandos portrait now in the NPG, and the Droeshout engraving, is that they don’t seem to suggest divine genius. The belief that intelligence could be measured in the features is almost as old as mankind. It’s only very recently that we’ve come to agree with Shakespeare that, on the whole, ‘there’s no art to find the mind’s construction in the face.’ Actually we don’t really agree with that either. We just look for a different set of psychological markers which, being our own, we find wholly convincing. But you know what I mean. Shakespeare nails it again. Look not on his picture, but on his book.

Gainsborough’s portrait, like Roubiliac’s bust that inspired it, or Kaufman’s portrait a few years later, would turn the raw material of Shakespeare’s features into an expression of boundless wisdom and humanity, shining with the inner light of the soul. But as far as I knew, Gainsborough’s portrait never got further than this pen-sketch in his letter.

Not so. Dad emailed me this mysterious likeness, sketched out before Gainsborough overpainted it. (X-ray image from Martin Postle ‘Gainsborough’s Lost Picture of Shakespeare’ Apollo December 1991 pp 374 – 379 ill.p 375).

Shakespeare is receiving heavenly inspiration, very like a saint in an Old Master painting.

St Matthew by Caravaggio.1600 (San Luigi dei Francesi, Rome)

The curious thing is that this language works its way into the picture that Gainsborough painted on top, the magnificent portrait of his friend, the composer Johann Christian Fischer (Royal Collection)

(c) Her Majesty the Queen

This is a more typically Gainsborough portrait, and far more satisfying. It is still an artist looking for inspiration, but the sitter’s air of patient forbearance, suggests that even genius doesn’t always strike on cue. This is a human being, not a vessel taking dictation from God, and the impression of warmth and humour produces a far better portrait. Both qualities apparent in the Chandos portrait of Shakespeare, which for my part I’ve always found the perfect expression of Shakespeare’s personality.