Humidity, not just light, key threat to glow-in-the-dark art

Conservation scientists have identified humidity as a primary driver in the breakdown of phosphorescent materials, a finding that could reshape how museums store and display glow-in-the-dark artworks. The research, presented at the American Chemical Society meeting in Chicago, focuses on preserving the vibrant colours found in mid-20th-century fashion and art, specifically works by the late designer Stephen Sprouse.

The study is a collaboration between Sarah Schmidtke Sobeck, a photochemist at The College of Wooster, and Gregory Smith, a conservation scientist at the Indianapolis Museum of Art at Newfields. The pair have worked together for the last decade to understand the unique photochemistry of these materials. Their earlier work on fluorescent pigments showed that optical brighteners degrade faster than the dyes themselves, causing colours to appear duller over time even if the pigment structure remains intact.

The current research extends this investigation to phosphorescent pigments, which differ significantly from their fluorescent counterparts. While fluorescent colourants typically rely on organic dyes to convert ultraviolet light into visible light, phosphorescent materials are composed of mineral-based pigments and inorganic compounds. These materials absorb energy when exposed to light and release it gradually as re-emitted light, creating the characteristic glow.

Sobeck noted that for artists, the visual impact of these colours is intentional rather than merely cosmetic. Sprouse’s collections from the mid-1980s, which blended graffiti prints with bright Day-Glo colours, are a prime example of this aesthetic. The Indianapolis Museum of Art at Newfields holds several such pieces in its textiles collection, making the preservation of these specific pigments a priority for the institution.

The findings indicate that humidity is a significant factor in the degradation of phosphorescent pigments, potentially as much if not more so than prolonged exposure to light. This distinction is crucial for conservationists, who must now adjust storage and exhibition practices to control moisture levels alongside light exposure to prevent the colours from fading.

The project is ongoing, with the next phase focusing on the white pigment powder lithopone. Researchers will test how long phosphorescent materials containing this specific pigment continue to glow after each charge, aiming to further refine the long-term restoration strategies for these unique cultural artefacts.