Deserts turned to glass

Abstract

Located in Apple Park in California (USA), Mirage is an outdoor sculpture of 448 solid cast glass cylindrical columns, each 210cm high and 15cm in diameter, made from 70 different desert. sands. The sculpture by Katie Paterson and Zeller & Moye involved a large team of artists, architects, geologists and scientists. This paper discusses the experimental work conducted by TU Delft on devel-oping glass compositions of the desired colour, hue and tint, as a function of foreign, impure sand addition to the basic batch recipe. XRF and XRD analyses of the desert sand samples revealed their chemical composition and crystallographic structure, purity level and presence of undesired con-taminants. Repetitive melting experiments led to establishing relationships between the sand character-istics and the colour hue, tint and intensity of the resulting glass, concluding to 0.02-17% desert sand content as substitute of the original, low-iron sand in the batch recipe. Iron oxides were identified as the prevailing colour agents, yielding a colour palette of blue, aquamarine and green hues based on their oxidation state. The melting experiments led to the formulation of a glass recipe prediction model and to modifications of the standard batch, towards achieving the desired colour gradient while preventing critical defects in the glass. The vertical casting of the columns by the glass studio gave a distinct surface pattern with recess lines and a high bubble content. To identify if the strength is governed by the surface quality, the bubble content or the glass's chemical composition and to attain representative strength data, 4-point bending tests were conducted on 37.5x51x635mm beam specimens produced by the same foundry. Fractography analysis of the tested specimens showed that the characteristic surface pattern governs the design strength. Mirage was inaugurated in May 2023, showcasing the potential and versatile beauty of using a wide range of impure sands in glass making.