Photo attribution: “headless statue” by is licensed under CC BY 2.0

My name is Dorothy Cheng and I am currently a Materials Conservation intern at NCPTT, working on a project investigating and comparing six commercially available anti-graffiti coatings for outdoor marble. I am a 2015 graduate of the MA in Conservation Studies program at West Dean College, in West Sussex, England. I specialized in metalwork conservation in graduate school, and happily this current project has incorporated some of my past research on the possibility of using anti-graffiti coatings for Corten weathering steel.

It’s usually preferable to avoid using coatings on historic, artistic, and cultural heritage, but sometimes marble monuments and sculptures are in graffiti-prone locations and/or represent controversial parts of our country’s history. The artistic culture and social commentary represented by some kinds of graffiti is a fascinating and controversial topic in itself, but that is a topic for another day and another blog post.

Graffiti materials such as aerosol spray paint and the ever popular Sharpie marker seep easily into porous marble surfaces to create stains (called ghosting) that are difficult to safely remove. Cleaning processes to completely remove ghosting can result in microabrasion and surface losses. An ideal coating preserves the natural color, gloss, texture, and integrity of marble substrates and adequately aids in the complete and safe removal of graffiti. Sacrificial coatings are reversible barrier films that can protect vulnerable surfaces from damage resulting from this type of vandalism. Sacrificial coatings are also attractive for health and safety reasons because many require only hot water washing for removing graffiti from coated surfaces. Avoiding the use of solvents and chemical cleaning agents is always a perk for the person carrying out the cleaning treatment!

The suite of tests I am currently running is aimed at evaluating the coatings’ aesthetic impact and effectiveness in facilitating graffiti removal from Royal Danby marble samples. Data is being gathered in the lab using colorimetry, glossimetry, laser profilometry, and contact angle goniometry to quantify how the substrate changes as the coating products are put to use. I will also be surveying local members of the community and asking them to visually assess and offer their honest opinions on the performance result of these coatings.

The coatings evaluated in this study are PSS 20, APP-S (also known as Stonewalled Sacrificial in the US), Protectosil AQUATRETE®SG®, “World’s Best” Graffiti Coating, Graffiti Melt, and Graffiti-Pruf. Each were either chosen due to notable performances in other studies, or their recommendation for use on other types of stone/masonry by experienced conservation and preservation professionals. Red spray paint and black Sharpie marker will be applied to the samples and removed according to the coating manufacturer’s instructions. Half of the samples will be placed in a QUV accelerated weathering chamber before attempted graffiti removal to assess the long-term effectiveness and reversibility of the coatings after artificial aging. Surface pH levels of the coatings before and after artificial aging will also be measured. I hope that the results of the study will help conservators caring for marble outdoor heritage select the most appropriate sacrificial coatings for their needs.

To learn more, please check out the second post about this study.

Intern Dorothy Cheng polishing marble samples before testing.

Intern Dorothy Cheng polishing marble samples before testing.

airless sprayer coating application

Dorothy Cheng applying a coating on marble samples with an airless sprayer.

Dorothy Cheng applies a coating on marble sample with a brush.

Dorothy Cheng applying a coating on marble sample with a brush.


National Center for Preservation Technology and Training
645 University Parkway
Natchitoches, LA 71457

Email: ncptt[at]
Phone: (318) 356-7444
Fax: (318) 356-9119