Interesting article on using air pockets to mark and track 3D printed objec= ts. http://www.theregister.co.uk/2017/07/21/watermark_3d_printed_plastic_with_a= ir/ The referenced paper also has a page and a half of interesting looking refe= rences. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .