Measurements of the fundamental ac-susceptibility provide a sensitive tool to study the shielding behavior of ceramic high-T c superconducting material. In this work, ac-susceptibility data for differently prepared YBaCuO-samples are presented. From the data, information can be extracted about an effective grain size, which is not necessarily identical to the optically determined particle size. It is demonstrated that the data allow an estimation of the bulk quality which depends strongly on the preparation conditions.