What do they look like?

Toughened glass droplet colloquially called a ‘Prince Rupert’s Drop’
© The Board of Trustees of the Science Museum

Three fire extinguishers containing hazardous substances carbon tetrachloride and BCF
© The Board of Trustees of the Science Museum

Above: shattered remains of an imploded glass triode valve
Below: the same valve during conservation
© The Board of Trustees of the Science Museum