During the Italian Renaissance, glassblowing flourished, especially in Venice. Antonio Neri, a Florentine glassmaker and priest, published his work L’Arte Vetraria in 1612, in which he described detailed recipes for making colored glass. We learn how oxides – such as iron – were used to give glass a rich green color.

Glassblowers perfected these techniques on the island of Murano: in red-hot furnaces, at temperatures well above 1000 °C, sand, ash, and metal oxides were melted into a glowing, viscous mass, which was blown, cut, and polished by master craftsmen. Green glass adorned windows, drinking vessels, and mirrors—and bathed rooms in a soft, soothing light.

Initially, this play of colors was pure luxury, intended for the nobility and colorful church windows. However, in the 18th century, green glass made its debut in the field of eye health for the first time. Around 1752, English optician James Ayscough experimented with blue and green eyeglass lenses. His goal was not fashion, but comfort – he was convinced that colored glass could soften harsh light and thus relieve “weak eyes.” This was the first step toward using color for a specific effect – an idea that would later be further developed in color therapy.