The aim of the proposed topic was to research the effects of UV thermochromic printing inks and to propose, by performing a detailed colorimetric analysis, a methodology of use and the characterization of these colours. Twelve thermochromic printing inks of various activation temperatures, producers and physical characteristics were analysed. By examining the physical characteristics of thermochromic inks and treating the samples by oxygen plasma, insight was gained into the thermochromic capsule's stability with respect to the binding material. Thermochromic pigment particles were analysed using a scanning electron microscope (SEM). A methodology has been developed which provides a unique instrumental method for determining the exact model of colour change and the temperature at which this change occurs. The possibility of carrying out colorimetric measurements of thermochromic colours under controlled conditions whereby a high repeatability of measurements necessary for quantifying the dynamic characteristics of thermochromic colours would be ensured has been confirmed. In order to demonstrate how thermochromic printing inks change colour with temperature, spectral reflectance curves and CIELAB colour space were used. The characteristic temperatures that define the reversible process of discoloration and coloration have been determined for thermochromic printing inks. Spectral reflexions of TCX samples were measured during three different cycles that vary depending on the temperature area within which the samples were measured. Results show that the colour of a thermochromic sample depends not only on temperature but also on its thermal history. A model for calculating the 3D space of the hysteresis loop was developed in order to see how reversible the samples really are. The stability of thermochromic ink within the hysteresis loop was analysed in detail. It has been confirmed that the degree of polymerisation during the UV drying of prints can influence the colour of a print in the coloration and discoloration state. By mixing thermochromic inks, new inks were obtained that besides exhibiting different dynamics of colour change, have better characteristics. It has been proven that the process is not indefinitely reversible and that there are factors that can destroy this process and undermine the functionality of thermochromic inks.