First person: 'I bought a Gainsborough on eBay'

Philip Mould, 49

There was a time when art dealers had to sneeze their way through auction rooms in order to unearth the right piece, but the work of a sleuth has changed in recent years. Today, we do much of our work in front of a computer screen. So it was, on this particular day, that I flicked through the pages of eBay. Suddenly I was struck by a small thumbnail image; it was billed as An American School Portrait of an Unknown Man. Other than that there was nothing – apart from the guide price of $100 (£62). Something about it jumped out at me, though; it exuded a certain glow that differentiates the work of Gainsborough from his contemporaries.

I was struck by a sense of curiosity, bordering on disbelief, as I waited for a larger image to load on my screen.

In this business, every picture is like a crime scene: we need to know who did it, how it was done, how much of what you are seeing is true and how much is fabrication. In the case of this picture, it soon became clear that if the head was genuine Gainsborough, the body was very much fabrication. Compared to the head, which was beckoning, the torso was rigid, like a pub sign. It was anatomically implausible, and aesthetically at odds with the face. I decided to bid, not quite knowing what I was going to find, and bagged the painting for £120.

As an art dealer you cannot speculate; you can only start applying your energies once you know what you're working with, and so I suspended my curiosity until the FedEx delivery arrived, two weeks later. When it came, I tore the package open and was presented with what was clearly a head of Gainsborough and the body of a strange, amateur-looking artist. It was almost like some insect having hatched from the larval stage. Then, due to an almost choking excitement, I did something I'd never recommend: I took out a bottle of acetone, and got to work.

It was the end of the day and the phone had stopped ringing. I was alone in my gallery and darkness was falling; that nice time when distractions are cloaked. I began slowly at first. As the fumes from the acetone kicked in, my fears and inhibitions about not destroying the painting began to lift. I stripped the layers of paint bit by bit. It was remarkable. Slowly a body and clothing that matched the elegance of the head began to emerge from behind the layers of added paint.

Within half an hour, the floor was strewn with wodges of cotton wool, thickly saturated with this horrible later paint, and I began to feel sure that this was an early Gainsborough that someone had superficially mutilated. I had a short, sharp shock at one stage when I saw pink colour coming through, thinking I'd over-cleaned it; but thankfully it was the edge of a hand demurely parked in the subject's waistcoat.

It took two hours to complete, and then, amid the chaos that had become my studio, it stood, like a freshly caught fish smiling back at me. I imagine that at some point in the past 50 to 100 years, someone had attempted to fix a tear in the painting. Once they'd knitted together the paper, I imagine they'd disguised their handiwork by painting over the area and went into overdrive. They probably had no idea what they were dealing with.

The following day I took the piece, rather sheepishly, to my restorer. She knew exactly what I'd been up to. We nicknamed the piece Mr eBay, as we have no idea who he is, though one day we hope to find out. Finding him has been a thrilling experience, and has given me a thirst for restoration. In idle moments I think how lovely that life might be, but my gallery colleagues don't agree. They now treat me like a drunk, hiding my acetone so I don't do anything like that again.

'Sleuth: the Amazing Quest for Lost Treasures', £20, published by Harper Collins