avoided catastrophe
In the early 90's at college, the "anachists' cookbook" textfile appeared on the network. and it was read by lots before the sysadmin deleted it.
One section, the "How to Make Thermite" stuck in mine and my mate's head. An easy recipe. Equal parts aluminium and iron oxide and a bit of magnesium ribbon to get it going.

Fast forward about 13 years and my mate gets a part time job as a lab technician at a college.
I went round to visit him one night and after a few beers he announces "Guess what I've accrued from college?"
"Job satisfaction?" asked I.

He wandered off into his garage and comes back with two small polythene bags containing a grey powder and a brown powder, and also a strip of magnesium ribbon.
"O-ho!" said I.
He fishes out an old clay plantpot and pour the powders in, gives it a mix and sticks the ribbon in as a wick.
He leans over with one of those long gas-match things you use to light the cooker when the sparky thing's knackered.
The ribbon glowed and then went nova. We shuffled back a bit and watched as the ribbon burned down to the powder. Now, barely able to see, the ribbon reached the powder and went out.
ARSE!
He fished the remaining ribbon from the powder, lit it again and it went out.

We gave up then and he disposed of the obviously inert powder, though he did manage to boot the plantpot over and leave a large rusty stain on the lawn which he managed to hose away before his wife came home the next morning.

Thinking back, I hate to think of the mess it would have made of his garden if it had gone up. There must have been a good-sized mugful amount of powder in the pot.
( sandettie light vessel automatic New Twitter - @bollocksreally, Tue 29 Jul 2008, 14:23, 4 replies)

Better than Magnesium...
A Sparkler will do the job, it burns longer and just as hot as magnesium.....
(Jimmy Large Is huffing Jenkem on, Tue 29 Jul 2008, 14:34, closed)

Hmm
This experiment actually works better (as I have found through some experimentation) if you put a small pile of magnesium around the magnesium ribbon.

Sadly, I never got it to work with copper oxide and aluminium powder.
(Potty Jag har smör i min rumpspringa, Tue 29 Jul 2008, 15:18, closed)

Our chemistry teacher showed us that
It was supposed to produce a trickle of molten iron out the bottom of the flowerpot into the brick below. Instead it exploded dramatically.

Undeterred we gathered the next week and he tried again. Another flowerpot bit the dust.

Probably not as dangerous as the time they tried to show us hydrogen and oxygen combining to make water, which was supposed to power a 2-litre bottle like a rocket. Nothing happened, so (luckily!) we all turned and started walking away. After we'd walked a few metres away we heard the biggest explosion I have ever encountered. There was no trace left of the experimental equipment.
(Skittlemcfluff ......................, Tue 29 Jul 2008, 16:44, closed)

Thermite
I did manage an Airfix paint tin of Copper Oxide/Aluminium once, detonated electrically from some distance, completely silent fireball of brilliant incandescent white about six foot across. Must try a big one some time.
(Benzyl, Wed 30 Jul 2008, 3:52, closed)