Method for modifying the surface state of materials, in particular of the paper and/or card type

A method of modifying the surface state of a print medium, the method comprising the steps of:

• simultaneously applying a plurality of printing fluids on the surface of the print medium in such a manner as to provide dusting zones on the medium suitable for retaining dusting powder particles which adhere exclusively on said zones;
• dusting a dusting powder onto said medium including said dusting zones;
• removing excess dusting powder by means of a flow of air;
• and heating the medium to fix the printing fluids and the dusting powder particles retained thereby, said heating being equivalent to the use of radiation at a wavelength of 2.5-3.8 .mu.;
• wherein said dusting powder is constituted by a substance which melts on heating and which is set after subsequent cooling, and wherein said heating step is performed in an atmosphere of hot air at a temperature of at least about 115.degree. C. sufficient to melt said dusting powder and having a degree of humidity not less than 85% and sufficient to counter a large drop in the humidity of the medium under the effect of the heating, the temperature of the surface of said print medium not exceeding about 90.degree. C. during said heating.