I like doing this demo every year but I do it outside (it does smell a bit and since fire is involved and since I've set off the fire alarms once too many times I've been banned from
using fire in the building...). Ammonium Dichromate is orange and I should have taken a
"before" photo (sorry!). Once it starts burning (my little wick ignited it quickly) the powder
makes it look very much like a volcano and this sequence of photos does not do it justice.
The final greenish powder is very fluffy and easily blown away so care must be taken not
to be in an area exposed to wind (or children who feel compelled to blow in the pile of ash!)