Glass, optics and IYOG: opinion

Abstract: How glass objects have evolved from simple artefacts valued for their appearance to sophisticated devices that have transformed our lives through their ability to manipulate light.

Optical properties are the beating heart of glass technology [1–5]. Imagine the amazement of early technologists who discovered transparent, solid droplets in the ashes of their fires—sand grains whose light scattering boundaries had surrendered their identity to a uniform melt. Over time they trialled new raw materials, optimising proportions, processing and properties. They found minerals that added colour and that the magical combination of colour and transparency mimicked precious stones. New industries supported an international trade in coloured beads. The Romans extended these skills, generating artwork worthy of its place in today’s international museums [6]. From 1000 AD, throughout Europe cathedrals appeared with stained glass windows protecting from weather, admitting light and illuminating bible stories with images readable by rich and poor alike. Later, coloured bottles signified ownership, warned of dangerous contents or protected from damaging UV radiation, while traffic lights and airport runway lighting using coloured glass filters created safer travel [7].

Off-colours naturally suggested poor quality. The Romans sourced the purest sands for fine tableware and knew that Mn-rich minerals reduced its green hue; they didn’t know the cause: a redox Fe2+ /Mn3+ interaction on cooling (reversible in strong sunlight!). Of course, glasstransparent in the visible nevertheless absorb IR and UV light. The greenhouse effect arises from the easy transmission of sunlight through glass which then traps the longer wavelengths emitted by the cooler objects inside. Controlling this helps minimise our need for heating in winter and cooling in summer. Now, smart glazing with selected coatings (low-e, solar control films) helps achieve it. [1,8]

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