A composition

A composition comprising:

• a near-infrared radiation absorbing compound;
• a colour-forming compound;
• and a heat transfer agent operable to facilitate heat transfer from the near-infrared radiation absorbing compound to the colour-forming compound;
• wherein the ratio of near-infrared radiation absorbing compound to heat transfer agent in the laser-reactive composition is 1:1 to 1:100, and the heat transfer agent is present in the composition as solid particles.

A composition comprising:

• a near-infrared radiation absorbing compound;
• a colour-forming compound;
• and a heat transfer agent operable to facilitate heat transfer from the near-infrared radiation absorbing compound to the colour-forming compound;
• wherein the heat transfer agent is selected from a metal oxide, a metal pyrophosphate, and a metal phosphate, and the heat transfer agent is present in the composition as solid particles.