A mask structure and method of quantitatively measuring pellicle degradation in production photomasks by measuring overlay in test structures on the mask. A structure is located in a high transmission region close to a transition region between a low transmission and a high transmission region of the mask such that pellicle degradation impacts the printing of the object. A second structure is located in low transmission region such that the printing of the second structure overlaps the first and provides a measure of pellicle degradation.