Red iron oxide is a common colorant used in the production of fireworks. It is a pigment that is typically made by roasting or calcining iron ore, which produces a reddish-brown powder.
It is often used to create bright red or orange-red hues in the pyrotechnic display. It is added to the pyrotechnic composition in small amounts, typically around 5-10% by weight. When the fireworks are ignited, it reacts with the other chemicals in the composition to produce a vibrant red color.
It is used for thermite, a mixture that produces enormous amounts of heat, forming molten iron. Due to its catalytic properties, it is also added to primes, and even colored star compositions to increase their ignitability and burn rate.
This is not particularly toxic or dangerous. It does, however, stain surfaces and textiles.