Hello For years we have calibrated our glass instruments (pipettes, volumetrics, and graduated cylinders) and we have identified their calibration status by marking a "C" in the instrument body. Having hundreds of such instrument, it would be difficult to identufy all of them independently The fact is that one of our customers has requested that all of our glass instruments be marked independently as a way to track their calibration status. As our policy has always been to satisfy the customer to the maximum extense possible, I've been tasked to find a solution. Those instruments do not have serial numbers. The glass instruments are very often autoclaved, heated to 250 °C, cleaned using strong acids or alcalis, so my question is: Is there a way to identify each of our glass instruments?. Does anybody has experience in this field? On the other hand, is there any regulation about this? Any help most welcomed. Thanks in advance.