In 2004, the Department of Veterans’ Affairs, National Cemetery Administration, and the National Center for Preservation Technology and Training entered into an interagency agreement to compare the effectiveness of commercially available cleaners for the removal of soiling and biological growth from Federally-issued headstones. The project goal was to test cleaning products for effectiveness and appropriateness and to make recommendations of products and methods best suited to both clean and preserve the headstones. Main tasks associated with the project were outlined in a project proposal and include both field and laboratory testing over a two-year period.
This study incorporates five national cemeteries that are distributed both geographically and climatically. Cemeteries included in this study are Alexandria National Cemetery in Pineville, LA; Bath National Cemetery in Bath, NY; Jefferson Barracks National Cemetery in St. Louis, MO; San Francisco National Cemetery, in San Francisco, CA; and Santa Fe National Cemetery, in Santa Fe, NM. Cemeteries were chosen to represent various regions of the National Cemetery Administration as well as different climatic zones. The cemeteries include sub-tropical, temperate, continental, semi-arid, and oceanic climates.
Water and five commercially available cleaners, including D/2Antimicrobial cleaner, Daybreak cleaner, World Environmental Group Marble cleaner, H2Orange Grout Safe cleaner, and Kodak Photo-Flo were evaluated at each test cemetery. Cleaners were applied to test patches on headstones carved from Colorado Yule marble and White Cherokee Georgia marble. Testing also included sunny and shady locations to help account for possible differences arising from local environmental variations.
Phase one of the study focused on field trials and ran from April 2005 to November 2006. Changes to headstone test patches as a result of cleaning with test cleaners were evaluated by appearance change and biological activity. Appearance changes were documented using photography and color measurements. Biological activity was documented initially and at six and twelve months after cleaning by enumerating bacteria, fungi and algae taken with BBL culture swabs from a three cm2 area from each test patch. The color measurement data was evaluated by calculating the frequency of color changes where ΔE was greater than 5 and where ΔE was greater than 10. These values represent changes that may be perceived by the human eye. Biological activity was presumed to reflect the re-growth of micro-organisms six months after cleaning (June 2006). The performance of test cleaners was evaluated based on biological activity and was ranked from one to six, with lower numbers indicating poorer performance. Biological activity was again evaluated twelve months after cleaning (February 2007) and the performance of four cleaners were evaluated and ranked.
Based on appearance change data and biological activity data, Kodak Photo-Flo was eliminated from further testing after six months. The greatest number of appearance changes for ΔE greater than 5 and ΔE greater than 10 was seen on test patches cleaned with Kodak Photo-Flo. This product was a poor performer at controlling bacteria in both sunny and shady locations in all cemeteries. It also ranked the lowest of all cleaners in limiting biological activity overall.
H2Orange Grout Safe cleaner seemed to perform well based on color measurements and performance rankings of biological activity after six months. However, closer inspection of photographs taken from Jefferson Barracks National Cemetery indicated that biological staining was present on the edges of the headstone patches cleaned with H2Orange Grout Safe cleaner. The location of the staining was not near the location of color measurements and was not reflected in the biological activity. Twelve months after the cleaning, all stains had disappeared. Researchers hypothesize that the H2Orange Grout Safe cleaner did not kill all microbes initially and it took some time for all growth to die. Use of H2Orange Grout Safe cleaner left an undesirable surface appearance for a period of time and thus was eliminated from the study.
Water and three cleaners remained ñ D/2 Antimicrobial cleaner, Daybreak cleaner, and World Monument Group Marble cleaner ñ as the project moved to phase two of the study. Appearance and biological activity continued to be documented for these cleaners in November/December 2006. Since further cleaners were being evaluated and the data from biological activity was more variable, few differences were noted. D/2 and Daybreak performed similarly in controlling overall biological activity. Researchers are concerned about possible chemical and physical changes from these cleaners, which are still under investigation.
Laboratory studies, including two accelerated weathering studies, were initiated. The first weathering study involved all six cleaners and two marble types. Lab test stones were cleaned on a daily basis for 33 days while being exposed to UV light, temperature cycles, and condensation cycles. These results were later considered to be too harsh, and a second accelerated weathering study was performed. In the second study, lab samples of Colorado Yule marble were cleaned and rinsed four times throughout the 33 day exposure.
Accelerated weathering samples are currently being evaluated for physical and chemical changes. Physical changes are being documented by changes in surface texture, color, and porosity. Chemical changes are being examined by optical microscopy, X-ray fluorescence spectroscopy, scanning electron microscopy, and determination of total soluble salts using gravimetric and conductivity methods. Accelerated weathering samples cleaned with D/2 and Daybreak show some evidence of efflorescence which is being investigated.
Lab test samples were placed beside field test headstones during phase one of the study. They have been retrieved and were received at NCPTT on April 2, 2007. They will undergo evaluation similar to that described for accelerated weathering samples above. Phase two of the project will continue through fall 2007. A student intern will be assigned to assist in the analysis of lab and field test stones.
Researchers associated with the project, including scientists at NCPTT and biologists at the Laboratory of Applied Microbiology, Harvard University, are concerned than an eighteen month time period may not have been sufficient to document significant visual changes or to allow for the growth of algae and photosynthetic bacteria. The absence of algae and photosynthetic bacteria is significant. These organisms typically provide the most visual evidence of growth on headstones. Their absence, even from stones treated with water, suggest it is still too early to determine the effectiveness of any biocidal properties of the cleaners.
While some results can be obtained by the expected completion date of October 2007, continuation of the study for two additional years is recommended. NCPTT staff present four possible options for continuation and the study in this report, and other options are available. It is advisable that some decision regarding extending the study be made prior to June 2007 (the date of the final field trip to the cemetery test sites).