Exhibition: Close Examination, National Gallery

If this exhibition were a TV series, it would be CSI (Grissom, not Caine) or maybe a high-end Hustle. If it were a book, it would a Dan Brown re-imagined by Ian McEwan. If it were a film it would be something starring a dashing prof played by James Stewart.

This is art with a magnifying glass, a cryptic clue, an unexplained anachronism and a journey towards the (occasionally very inconvenient) truth; it's classy, accessible and devilishly intriguing.

Not often do the backroom boys and girls with their gadgets and their hunches get to parade their know-how on the walls of the National Gallery.

Here, they do a nifty show and tell introducing visitors to practices such as cross section microscopy, pigment analysis, dendrochronology and infrared reflectography.

Tucked away in the Sainsbury wing, this compact display is like the Black Museum of the Met Police, where the dirty little secrets are aired and slip-ups find a new lease of life as warnings against wishful thinking.

One example of which is Botticelli. The master had only just been re-discovered in the late Victorian era when two works attributed to him came up in auction and were enthusiastically snapped up for the gallery.

An Allegory (in hindsight) is plainly an inferior work to Venus And Mars, lacking the precision, depth and texture. But the former, by an unknown, was bought for £1,627 10s and the latter, now one of the most beloved pictures in the collection, for much less - £1,050.

Oops. But in a good way.

At its heart, this remains a display of paintings as well as a detective's trail. So there are works by Durer, Gossaert, Rembrandt, Raphael.

And, of course, derivatives of the above - whether as fakes, homage, homework, riddles or a rebranding of a non-descript to boost the price tag.

But's not all hoodlum ruses and knock-off Nigels. There's a flipside. Saint Francis Of Assissi With Angels (1475-80), originally attributed to Botticelli pupil Filippino Lippi, on restoration is re-attributed to the master himself.

And the shimmering Madonna Of The Pinks by Raphael (1506-7) - pictured - was copied a dozen or more times. Scientific examination revealed the National Gallery held the original. Spontaneity gave curators a clue.

Save for a few microscopic flecks, the original plum colour of the curtains is lost beneath a new coat of green. The copyists were unaware of the artist's change of heart and applied just the green.

Greatness, restored.

– From July 2010