Abstract: “Advanced greyscale imaging analysis was conducted using Adobe Photoshop 6 on the surfaces of masonry stones and clay bricks, taken from old buildings, to accurately assess the efficiency of building cleaning. Five commonly used masonry stones and clay bricks for those buildings were selected, and seven abrasives were adopted for air abrasive (sandblasting) cleaning. Also the reductions in thickness were continuously monitored for assessing the cleaning efficiency. The cleaning degree at different stages was assessed using greyscale image photos, converted from original colour ones, together with reductions in thickness. In general, greyscale continuously increased with the cleaning time and tended to be stable when the surface became fully cleaned. Thickness reduction monotonically increased with the cleaning time. The most efficient building cleaning case would be the one with the shortest cleaning time and smallest thickness reduction. The harder abrasives with smaller particles size”

Keywords: historic building, masonry stones and bricks, air abrasive cleaning, greyscale, cleanness