Blue touch-paper

‘Light the blue touch-paper and retire to safe distance’ has been the standard safety warning on all fireworks from the late 19th century onwards. Touch-paper itself is paper impregnated with nitre (saltpetre) so that it burns slowly thus making it ideal for setting off explosives and dates from the mid-18th century. Since the early 20th century, ‘lighting the blue touch-paper’ has become a metaphor for causing a commotion or disturbance.