He interrupted. 'How does a metal detector work?
'Well,' I said, 'inside that flat white plate thing there is a coil of very thin wire. The batteries in that white box, when you switch them on, produce a high-frequency alternating current in the coil, which in turn produces an oscillating magnetic field which will induce a responding current in any metal near it, which will, in turn, excite the coil even more, whose increased activity can be interpreted as a whine - and that's putting it simply.'
'You've lost me,' Himself said.
'I had to look it up,' I agreed. 'It's a bit hard to understand.'
He looked around at all the little dug up heaps of unprecious metal.
'Well, yes,' I grinned. 'I buried a lot of things to keep searchers busy.'
'Really, Al.'
"The childish mind,' I said. 'I couldn't help it. I did it five years ago. I might not do it now.'
'So where is the hilt?'
'It's where I hid it when you gave it to me.'
'But where?
'Everyone talks about buried treasure…' I said, 'so I didn't bury it.'
He stared.
I said, The metal that most confuses a detector is a sheet of aluminium foil. So to start with I wrapped the hilt in several loose layers of foil, until it was a shapeless bundle about the size of a pillow. Then I took a length of cotton duck - that's the stuff I paint the pictures on - and I primed it with several coats of gesso to stiffen it and make it waterproof, and then I painted it all over with burnt-umber acrylic paint, which is a dark brown colour and also waterproof.'
'Go on,' he said when I paused. 'What then?'
"Then I wrapped the foil bundle in the cotton duck, and super-glued it so that it wouldn't fall undone. Then all over the surface I super-glued pieces of granite.' I waved a hand at the grey stony ground of the plateau. 'And then… well, the more metal you offer to a detector the more it gets confused, so I put the hilt bundle where it was more or less surrounded by metal…'
'But,' he objected, 'they dug up that whole old oven and the hilt wasn't in it…'
'I told you,' I said, 'I didn't bury it. I glued it onto the mountain.'
'You did… what?
'I glued it granite to granite, and covered it with more granite pieces until you can't distinguish it by eye from the rock around it. I check it fairly often. It never moves.'
He looked at the metal detector in his hands.
'Turn it upside down,' I said.
He did as I said, waving the flat round plate in the air.
'Now I'll switch it on,' I said, and did so. 'And,' I said formally, laughing, 'my lord, follow me.'
I walked not up onto the hill, as he obviously expected, but into my corrugated iron-topped carport.
The waving upside-down metal detector whined non-stop.
'If you go to the rear wall,' I said, 'and stand just there,' I pointed, 'you will hear the indistinguishable noise of the Honour of the Kinlochs, which is up on the carport roof where it joins the mountain. If you stand just there, the hilt of Prince Charles Edward Stuart's ceremonial sword will be straight above your head.'