| 摘要 |
The substrate for printing-writing comprises at least one metal salt which is coloured in the moist state and has a different colour in the dry state, incorporated into or onto the said printing-writing substrate, the quantity of salt in relation to the substrate, on a dry weight basis, being such that the colour of the substrate at ambient temperature is substantially the colour of a substrate which does not comprise a metal salt, and that the colour of the substrate is modified reversibly when the temperature of the substrate is raised. When employed by itself, the metal salt is not a cobalt salt. The substrate can be employed as security paper capable of being authenticated using heat and proof against tampering using a chemical agent.
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