The presentation Techniques and preparation materials in Portuguese painting of the fifteenth and sixteenth centuries is part of the integrated study of our PhD program, under the same title. The multianalitical methodology defined in this program, was possible through support of the project The invisible ground layer and its influence in portuguese paintings of the 15th and 16th centuries: a question to be settled (PTDC/EAT-HAT/100868/2008).The project included the reanalysis of ground layers of paintings previously studied in the Laboratório José de Figueiredo da Direcção Geral do Património Cultural (LJF-DGPC), as well as samples from paintings materially studied for the first time. Systematic analysis of the ground layers was performed in about a hundred paintings assigned to national workshops such as Viseu, Coimbra, Lisboa and Évora, including paintings with no specific author or workshop assignment. Results are presented from the constituent inorganic materials as well as the typological structures of the painting ground layers analyzed so far.