At last I’ve found out why the lighting in museums is often dimmer than a normal person would like. I was vaguely aware that it had something to do with preserving the exhibits (rather than the staff’s reluctance to clean in the corners) but now I’ve seen exactly why.

The team from Whitehall Roman Villa recently met some of the people whose job it is to see that all the lovely stuff in the display cases doesn’t fall to bits before our eyes. Just to make the point, one of the conservators lifted up what appeared to be a pile of rags resting on the table in her lab.

Enough of it still hung together to reveal that it had once been an elegant Victorian dress made of purple silk. The rest dangled in ribbons the colour of pale mud. The words ‘bodice-ripper’ came to mind.

In fact, nobody had touched this dress. It had been safely displayed in a glass museum case – by a sunny window.

We saw 20th century toothbrushes containing acids that were now burning their way through plastic storage containers while the conservators figured out what on earth to do with them. (My parents used to clean their teeth with things like that?!) .

We saw ancient iron that had been ‘protected’ – and underneath the coating, had secretly and silently rusted into nothing.

We saw a silk ‘handkerchief’ map issued to service personnel that needed nothing more than gentle ironing… except that the edges were bound with some unidentifiable gunk. The conservators knew, from bitter experience, that they’d better find out exactly what the gunk was before they interfered with it. And I haven’t time to mention moths, woodworm, mould…

I’d always assumed that once something was in its glass case, all the staff had to do was dust it. Silly me. Behind the scenes in the museum, war is being waged.

One last thing, in response to a dreadful rumour that’s come my way. Please, please, if you must metal-detect (and yes, I know there are some wonderful detectorists out there as well as scoundrels) – resist the urge to shine up your finds with Cillit Bang. It really isn’t the thing.