This dataset provides the data for the four glass standards used for monitoring the precision and accuracy of electron probe microanalyses (EPMA) during analytical runs of cryptotephra glass shards in sediment cores EMB201/13-4 and POS507/29-2. For each EPMA run, all four glass standards were measured. The major element composition of the glass standards was measured using a JEOL JXA-8230 electron microprobe at GFZ Potsdam, Germany (15 kV, 10 nA, 5-10 µm beam size). Instrumental calibration used natural mineral standards. Glass standards were Lipari obsidian (Hunt & Hill 1996; Kuehn et al. 2011) and MPI-Ding glasses ATHO-G, StHs-6-80-G and GOR-132-G (Jochum et al. 2006).