In the past forty years, outdoor murals have become a familiar feature in many cities in America, and around the world.	Murals are painted by a range of people, from community groups to professional artists. Murals have gained attention as important historic landmarks and as influential and often beautiful works of art. As cities struggle to save these significant artworks, serious preservation issues are coming to light.	Deterioration of outdoor murals is commonly caused by: weathering, pollution, and biological effects; interactions with building materials; interactions within the art materials; and from human interaction, such as graffiti.
Graffiti has existed for millennia with examples dating back to ancient Greece and Rome. Graffiti is now a recognized and often appreciated artistic style, XX complete with a recent retrospective at the Museum of Contemporary Art in Los Angeles called “Art in the Streets.”	However, when graffiti is applied to another person’s property without XX permission, it is illegal and a type of vandalism. Rapid removal may be the key to preventing graffiti. It is widely believed that graffiti artists move on from places where their work is not allowed to stay on view; rapid or immediate removal is the standard in mural preservation plans. Murals are a valuable part of modern society, and must be preserved so that current and future generations can benefit from their	An anti-graffiti coating is a clear coating applied over a mural that makes a barrier between the mural and graffiti. Anti-graffiti coatings differ from varnishes because they have specific properties that allow them to have graffiti removed from their surface without damaging the mural layer beneath. Anti-graffiti coatings can potentially protect a mural from the harms of graffiti.
The Getty Conservation Institute has been researching anti-graffiti coatings since 2008, beginning with a literature review and search for products currently on the market and used by artists, conservators, and cities for this purpose. Over one year, practical testing of a selection of anti-graffiti coating products was carried out on two test murals. The project was designed to simulate a conservation treatment in the field and in doing so, collect realistic results and useful observ	Three walls at the Getty Center, out of view from the public, were chosen as sites for three sets of two test murals, each set facing a different direction: west, east, and south.	To assess the functionality and effectiveness of the anti-graffiti coatings, XX a selection of graffiti materials was applied over the anti-graffiti coatings, and then the graffiti was removed using methods recommended by the coating manufacturers.
The murals were painted using two brands of acrylic paint commonly used to paint outdoor murals, Golden Acrylics and Nova Color. The murals are painted in a limited palette which represents three stable colors, three unstable colors, titanium white mixed with the unstable colors to make tints of the three unstable colors, and titanium white alone. The ten paint colors were applied in ten vertical columns of equal width, XX and the ten columns make one mural of the six total mur	Eleven coatings that are currently being used by conservators were selected for testing, and applied to the two west facing murals, one Golden mural and one Nova Color mural. Anti-graffiti coatings come in many different formulations. The coatings that we tested include acrylics and fluorinated acrylics, waterborne polyurethane, silicone, polysaccharides, and waxes. There are many types of anti-graffiti coatings but they all fall into one of two categories: permanent and sacrificial.	The coatings were applied in horizontal rows over the mural. Permanent coatings were applied on the upper section of the mural, and sacrificial coatings were applied on the lower part. Four columns on each mural were used to test four different time periods that the graffiti was left on the surface before being removed: removal of graffiti one day after its application, for 10 successive rounds; removal one month after; removal six months after; and removal one year after graffiti application.
Other important considerations when selecting the coatings were health and safety, and environmental impact. Volatile organic compounds, or VOCs, can be dangerous to human health and cause harm to the environment; and a major source of man-made VOCs are solvents in paints and protective coatings. with safe and sustainable standards, we wanted to use low or no VOC coatings; XX and of the 11 coatings included in the testing, 10 were in aqueous solutions.	Graffitists work with spray paint, markers, and even house paint shot through powerful squirt guns. Five representative graffiti materials were selected based on research into popularity and accessibility. As you can see in the diagram, the five graffiti materials each have a distinct color that contrasts with the mural paint for high visibility.	The goal of the project was to test anti-graffiti coating systems designed by manufacturers, so we used the specific recommendations for graffiti removal whenever possible. In an effort to be consistent with the low or no VOC standard of the rest of the project, we wanted to use the most environmentally friendly methods when we could.high pressure hot water could be safely used to remove graffiti from the permanent coatings, and to remove the sacrificial coatings along with the graffiti.
Some of the “permanent” coatings even came off under the high heat and pressure, leaving the mural uncoated after the treatment.We followed the high pressure hot water with solvent removal using the proprietary removers. Overall, the removers worked, however some of the removers were impossible to acquire because of VOC laws and other challenges. Though the removers that we did acquire worked well to dissolve the graffiti, they were also capable of dissolving the coating, and the mural paint.	The high pressure hot water sprayer had issues of its own, mainly the temperature and pressure of the equipment was not consistent, and the machines had limited controls for these parameters. Generally the permanent coatings perform better with high pressure, and the sacrificial coatings all have different temperature and pressure requirements. Some coatings did not respond to high pressure hot water at all. It should also be noted that high heat is innately unsafe for acrylic murals.	In fact, several of the mural test sections were damaged by the high pressure hot water, literally blowing off areas of paint from the mural. And, as I mentioned before, some permanent coatings were also inadvertently removed with high pressure hot water. At this point, without proper control, high pressure hot water is not a safe technique for cleaning murals.
The coatings were evaluated according to several criteria including: appearance, performance, and stability. The appearance category includes the color, clarity, and sheen of each coating. Both overall visual evaluation and colorimetry were used to compare the change in color between mural sections with and without anti-graffiti coatings, and in general, most anti-graffiti coatings made the mural appear slightly darker and more saturated. Some of the coatings attract dirt more than others.	In this study, performance includes: ease of application, ease of graffiti removal, efficiency of graffiti removal, and durability of the coatings during the removal process. According to these criteria, XX the sacrificial coatings outperformed the permanent coatings.	By looking at a picture of one 10-day column after 10 rounds of testing, most of the built-up graffiti residue is on the upper half of the test mural, where the permanent coatings were applied, and shows that permanent coatings underperformed in the experiment.
Pros and cons of anti-graffiti coatings.
By looking at the preliminary results of this experiment, the coatings with acceptable results include those highlighted on the table.	From this project we learned about the specific characteristics and behavior of a variety of coatings that are currently being used on murals. When evaluating anti-graffiti coatings, there are many factors to consider, and at this point in the project, the factors have been narrowed down, and we have determined specific characters of each coating. None of the coatings we tested have all the characteristics of a desirable anti-graffiti coating, but it is worth investigating products and methods	Right now, no single coating can meet all the requirements, so-- we could try a layered coating system or maybe even develop a new product. In conclusion: We know what we want in coating, we know that there is not one single coating that has everything we want, and now we need to look into other options.