My plan is to make a periscope - which has to be watertight. Sounds easy enough, but ‘they’ won’t let me use a mirror - I have to make one.

I’ve silvered glass once before – and I know it’s quite a sensitive process. Too high a temperature, too dirty a surface, or too many impurities in the mix – and it won’t work. So I was pretty keen to start today: I need time to get it to work.

But we have no silver nitrate and no ammonia! Mike’s making the silver nitrate, and also the alkali I need (potash - from wood burned in the fire). But ammonia, another key ingredient, just isn’t available on the island (not since September 11, 2001  - it’s too useful for making explosives).

So we have to make that too - from everyone’s pee. Marvellous! You can just buy ammonia in the UK in supermarkets.

Mike’s been a complete superstar - getting on making all the chemicals. I helped boil the urine down and boil the potash too. But mainly I got on and prepared the rest of the periscope.

I cut lengths of plastic tube, and eventually found tubes that fit each other reasonably snugly. I cut bits of glass to fit into the bend of a right-angled tube. I wanted the biggest bit of glass that still could fit into the tube. After experimenting with cardboard + polystyrene sheets - I decided on the octagons …Now I just need to silver them. Am not wildly optimistic!

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