Microprocessor-controlled analytical methods produce large amounts of data in a short time. This wealth of information is difficult to handle with conventional methods. Numerical classification is a valuable tool for reducing large arrays of data and revealing structure therein. Non-hierarchical methods have been used with good results for the classification of spectral analytical data of ancient glass samples. With the newly developed program APART, a classification was obtained according to technological aspects of glass production. The narrow clusters found were caused by local traditions and the use of similar raw materials. The coloring materials and decolorants contribute most to the trace element content, and are therefore dominant in the classification.