3.4. Evaluation Methods for Change in Appearance and Biological Activity

The emphasis during phase one was on the visual appearance of the stone before and after cleaning and on the amount of biological re-growth over time. The five cleaners were evaluated based on patches tests on stones in sunny and shady locations within each cemetery. These evaluations were used to eliminate or retain cleaners for phase two of the study.

The appearance of the headstone is defined as the outward or visual aspect of the stone and is considered a subjective judgment of the viewer. Since the appearance of the stone is particular to a given individual, it is influenced by cultural bias. In general, military headstones are expected to be clean, white, legible, and well-aligned. Thus unacceptable appearance includes gray, yellow, black, or mottled coloring from either biological growth, dirt, or chemical changes. In all phases of the study, two methods for documentation and analysis of appearance are proposed ñ use of photo-documentation coupled with visual ranking and color measurement.

Photography is the way information in the form of light documented from a subject, in this case a headstone. It is an easy way to document information from a site or location and covey it to others. However, the environmental variables and instrumental variables can affect the way the light is captured in the photograph. Thus, when documenting the headstones and cleaning patches with photography, some variability in the images will be due to the time of day in which the photograph was taken, and the camera settings (e.g. aperture, focal length, shutter speed, etc.). Also, the way in which the photograph is perceived varies from viewer to viewer. Because of these considerations, photo documentation is a qualitative method for studying appearance. One way to deal with this qualitative information is to have viewers rank what they see in photographs based on a set scale. The viewers should know little about the subject prior to the ranking, making them unbiased viewers. This produces a way to evaluate the information recorded in a photograph which is semiquantitative.

Being able to quantify the color and surface appearance of stones is a crucial factor in this study. Color is a physiological process by which the human eye translates electromagnetic radiation. It is generally dependent on the observer, the object, and the environment in which the object is viewed.

A colorimeter is an instrument that measures red, blue, and green color components of light and is used to determine a specific color reflected from a surface. The color is specified in numeric terms using the CIELAB color system. Colors are specified in terms of L^*, a^*, and b^*. The L^* values represent lightness and can range from 0 to 100, with 0 designating black, and 100 designating white. The a^* values represent the red-green chromatic component. Values of a^* range from -100, designating green to 100, designating red. The b^* values represent the yellow-blue chromatic component, with values ranging from -100 to 100. A pure yellow is represented by 100 and a pure blue is represented as -100 on the B^* scale.

The CIELab system lends itself well to measuring change sin color over time. The total color difference, ΔE^*, can be calculated from:

ΔE^* = (ΔL^*2+Δa^*2+Δb^*2)^1/2
ΔL^* is the lightness value difference between color 1 and color 2, = L^*₁ - L^*₂
Δa^* is the red-green value difference between color 1 and color 2, = a^*₁ - a^*₂
Δb^* is the yellow-blue value difference between color 1 and color 2, = b^*₁ - b^*₂
Equation 1. The total color difference between two Lab color measurements.

A total color difference of less than 2 ΔE^* is imperceptible to the human eye. Color measurements of L^*, a^*, and b^* are taken of the headstones prior to cleaning and documented. Since the surface of the stone is not completely smooth, three measurements are taken at each location then averaged. Measurements are repeated at each cleaning test site on regular intervals throughout the study.

A general overview of the biological testing is presented here. Details of the biological testing can be found in Appendix D, Appendix E, and Appendix F. The team determined the biological testing scheme for the study in consultation with Dr. Ralph Mitchell, Department of Engineering and Applied Science, Harvard University. Initially, NCPTT scientists proposed the identification of biological species present on a large number of headstones. However the actual number of samples to be taken and the time and effort to complete the biological analyses would have resulted in over 63,000 hours of work and was dismissed as untenable. Mitchell recommended general identification of bacteria, fungi, and photosynthetic microorganisms (algae) found on headstone prior to cleaning. Then, over time, counts of bacteria, fungi, and algae would be determined for test patches each cleaner in sunny and shady locations.

To determine the baseline biological activity, swabs are taken from a three cm2 area of each test patch using BBL Culture Swabs (Becton-Dickinson, Sparks, MD). Bacteria and fungi are enumerated by plating samples on solid media. Plates are incubated at room temperature for two days and colonies are counted. Photosynthetic microorganisms (algae) are analyzed using a hemocytometer. The numbers of algae in at least 10 fields of view are counted at 40X magnification.

Once the planning activities of phase one were complete, implementation tasks were begun. Jason Church initiated the first of a field trip series beginning in June 2005⁵ to each of the test cemeteries. The purpose of these first trips was to initiate contact with each cemetery staff, to identify headstones for inclusion, to set field test samples for phase two of the study, and to take overview photographs of each cemetery for the study.

All stones selected for inclusion in phase one were taped in a grid system that created six test patch sites.