These are pyrotechnic sprays, often referred to as fountains or flower- pots. They consist of a tube full of composition, sealed at one end and with a nozzle at the other, similar to a rocket. Unlike a rocket, they are not designed to move anywhere, so all the emphasis is on making the nozzle exhaust as long as pretty as possible, with large amounts of sparks, nice colours etc. The sparks are produced by metal powders or coarse charcoal in the gerb composition, with coarse titanium powder being the chemical of choice. Gerb compositions in a thin tube set up in a spiral arrangement are used as wheel drivers, for spinning fireworks e.g. Catherine wheels.