Dragon's eggs

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Dragon's eggs are pyrotechnic stars which first burn for a period giving a visual effect then explode with a loud crackling report. Manufacture of this effect has become controversial due to the heavy metals involved in the process, particularly lead tetraoxide (Pb₃O₄). Nowadays, bismuth trioxide is commonly used as a more environmentally-friendly substitute for lead compounds in achieving the effect, and its occurence in fireworks displays has since become much more common. Because of its chemical makeup, a shell or cake containing dragon's eggs as its primary effect is often noticably heavier than a similar device containing other effects.