Book excerpt: For more than 400 years, optical glass has provided mankind with a window into both the hidden microcosm and vast outer cosmos of the known universe, transforming philosophy, science, and engineering through its visage and, thus, shaping modern civilization. Its high transmittance, homogeneity, and precisely defined light refraction properties are the preconditions for highly resolved true-color imaging, making it an intrinsic component of technology in general. From consumer products, such as cameras and binoculars, to microscopes and telescopes-the most essential tools of research in many fields-the role of optical glass is integral to the very foundations of modern science and industry.