Monthly Summary May 2026

OVERVIEW

Physical work resumed on 18 May with four qualified restorers after more than two months of suspension. The team restarted systematic documentation and focused on removing persistent deposits from staircase masonry, vault plaster and marble, while opening a new conservation front on the altar mosaic.

KEY PROGRESS

• Continued thematic mapping and high-resolution photographic documentation of areas not previously treated.
• Deep-cleaned staircase stone with controlled cellulose-pulp and demineralised-water applications, followed by targeted cleaning agents, and removed incompatible cement-based joint fillings.
• Treated the historic vault plaster with a low-water ammonium-bicarbonate system to remove soot and sulphate deposits while limiting the movement of soluble salts.
• Tested removal of the later protective layer on marble; at this stage, acetone with 10% benzyl alcohol gave the most effective controlled result.
• Dismantled the altar's wooden support, documented deposits, lacunae, detached layers and mobile tesserae, and began the first mosaic cleaning tests on 22 May.

IN BRIEF: Removal of persistent deposits advanced across stone, marble and plaster. Mosaic cleaning had begun, with securing of mobile tesserae, edge protection and deeper consolidation identified as the next steps.