Agar Foam: Properties and Cleaning Effectiveness on Gypsum Surfaces

In the past decade, the usage of soft materials, like gels, has allowed for a better control of the water release process into the substrate for cleaning interventions. Agar-a natural polysaccharide harvested from algae-has been used to perform cleaning of stone materials, gypsum works, and paintings with remarkably positive results. Agar presents the great advantage of being cheap, easily available, fast to produce and not toxic, allowing for more sustainable conservation works. More recently, a new type of agar fluid, agar foam, promises further control of the water release and ease of application on delicate surfaces. In the present study, this new type of agar, CO2 and N2O foams, has been characterized and compared with the conventional sol/gel agar system. Moreover, the cleaning effectiveness of the agar foam was tested both in laboratory conditions and in two case studies: a historical gypsum from the porch framing of the Abbey of Nonantola, and the 20th century gypsum cast of the Pieta Rondanini by Michelangelo, located in the Sforza Castle in Milan. The obtained results show that foaming changes the sol-gel transition temperature of the agar gel as well as incrementing its dissipative behavior. When freshly applied, the foams flow with a reduced velocity, thus allowing a better control and ease of application. Once gelified, they act as a soft solid-like material, as shown by their rheological properties. Moreover, it was found that CO2 foam slightly reduces the water release to the surface, while maintaining the moldability and ease of application. The study allows for the conclusion that agar foam offers an interesting alternative for delicate surfaces, with a non-coherent mineral deposit, and with complex geometries that often represent a challenge for the conventional agar applications

Automated summary

In the past decade, the use of soft materials, such as gels and agar, has allowed for better control of the water release process for cleaning interventions. Agar, a cheap and easily available natural polysaccharide harvested from algae, has been proven to effectively clean stone materials, gypsum works, and paintings. A new type of agar, agar foam, offers even more control of water release and ease of application on delicate surfaces. The study compared agar foam with the conventional sol/gel agar system and found that the foam has improved dissipative behavior and can be applied with better control and ease. CO2 foam, in particular, reduces water release while maintaining moldability and ease of application. This study concludes that agar foam is a promising alternative for cleaning delicate surfaces with complex geometries.