Dragon's egg

A dragon's egg is a fireworks pyrotechnic star which first burns for a period for a visual effect then explodes with a loud report.

Manufacture of this effect became controversial because of the heavy metals once used, particularly lead tetroxide (Pb₃O₄). Nowadays, however, bismuth trioxide or bismuth subcarbonate are commonly used as more environmentally friendly substitutes for lead compounds to achieve the effect, and its occurrence in fireworks displays has since become much more common.

Because of its chemical makeup, a shell or cake containing mainly dragon's eggs is often noticeably heavier than a similar device containing other effects.