Stereolithography (SLA) 3D printing can create transparent objects that, with some post-processing, can be made optically clear. Formlabs' latest resin 3D printers, the compact and blazing fast Form 4 and the large format Form 4L, take clarity one step further by using a flexible resin tank that reduces peel forces, resulting in clearer parts with smooth surface finish. More info at https://formlabs.com/blog/3d-printing-transparent-parts-techniques-for-finishing-clear-resin/?srsltid=AfmBOopEyqOV