Quality improvement for mass production lines is an ongoing topic for many years. The target is to reduce the rate of defects and scrap during production having an impact on sustainability, delivery time and cost. For the example of mass lens production at ZEISS we introduce a Markov-based method, that allows us to trace the movement of a given product through the production line to help us understand potential root causes for quality losses and thus being able to predict defects. In the end we aim to achieve a closed loop quality control avoiding quality losses by an improved understanding of root causes and proactive actions enabled by Industry 4.0 technologies such as Machine Connectivity and Artificial Intelligence.