Innovation in Green Materials for the Non-Contact Stabilization of Sensitive Works of Art: Preliminary Assessment and the First Application of Ultra-Low Viscosity Hydroxypropyl Methylcellulose (HPMC) by Ultrasonic Misting to Consolidate Unstable Porous and Powdery Media

Paintings and other works of art created with fragile and mechanically unstable powdery media present challenges to conservators. Frequently, powdery media is water-sensitive, extremely fragile, tends to delaminate, and may be altered by even the slightest physical action or interaction with liquids. Materials that can provide an efficient stabilization without unacceptably altering the optical characteristics of the delicate substrate are extremely limited. Among these, Funori, Isinglass, and Methocel A4C have become established for this use. In bench practice, consolidants are frequently applied in a non-contact way, using ultrasonic and pneumatic aerosol generators to minimize the impact of the consolidant on sensitive substrates. However, nebulizing the available materials is problematic in bench practice, because of their high viscosity and, only extremely low concentrations can be nebulized using low kinetic impact ultrasonic or pressure-based misting systems adopted from the healthcare industry. As a potential innovative solution, this study introduces novel ultra-low viscosity (ULV) cellulose ethers (ULV-HPMC) for stabilisation of unstable porous and powdery surfaces, which have been successfully applied in bench practice for the pilot treatment of Edvard Munch painting on canvas and two 19th c. Thai gouache paintings on panel. Novel ULV-HPMC materials have multiple desirable qualities for consolidation treatments in conservation, and in accelerated aging tests marginally outperformed Methocel A4C, considered to be one of the most stable consolidants in the practice of conservation. Because of the ultra-low viscosity, higher concentrations of ULV-HPMC materials can be applied as water-based aerosols in a non-contact way and in fewer applications, which is a significant advantage in the treatment of delicate water-sensitive surfaces. Notably, novel ULV biopolymers are low-cost, derive from sustainable and renewable sources, and do not raise health and environmental concerns. Such novel materials and methods seamlessly resonate with the ICOM-CC’s Melbourne 2014 declaration, EU Green Deal, and the UN’s Sustainable Development goals and show potential adding new sustainable materials with the exceptionally low viscosity to the conservator’s tool box.