The terra sigillata of good quality (TS) and that of bad quality (TH) from the workshop of La Peniche (mid-1st century A.D.) are of similar mineralogical, chemical, and porosimetrical composition. Both are very Ca-rich products and differ markedly from other terra sigillata workshop products; differentiation was made with the CaO/MgO, Ba/Cr + Ni, and MnO/K₂O ratios. The good fired products show the paragenesis basic plagioclase + diopside + quartz + hematite + glassy matrix (± wollastonite); illite is only present in lower fired sherds; calcite is clearly secondary (decomposition of gehlenite or immigration after the bury). Firing experi-ments and porosimetric investigation infer that the TS has been fired at 1000-1050° and the TH at 950-1000°. -- AATA