Jason Church began cleaning headstones after (1) documenting their visual appearance
using digital photography and colorimetry and (2) sampling their surfaces for biological
activity.
Figure 5. Jason Church applies WEG Marble Cleaner to a taped test patch. He holds a piece of
acetate to the stone surface to prevent runoff below the patch. All cleaners were applied following
manufacturerís recommendations for dwell time, etc. The stones were subsequently rinsed with
water, again using the acetate to prevent runoff.
A grid was taped onto each stone using one inch wide 3M blue tape. Cleaners were
applied to the surface of the headstone following manufacturersí recommendations. An
8.5 x 11 inch acetate sheet was used to insure that cleaner did not run to a second test
grid. If the stone had raised or engraved lettering, the acetate was taped to the irregular
surface. Cleaners were applied in the same test grid on each stone, as shown in
Illustration 1 After each test patch was cleaned, the area was thoroughly rinsed with tap
water.
Illustration 2. This illustration shows the position of each cleaner
on a headstone.
3.5.4. Appearance Changes
Based on visual observations, all cleaners effectively removed soiling and biological
growth from the stone. Water removed soiling and to a much lesser extent staining from
micro-organisms. Changes in appearance were recorded by photographs and color
measurements. In general, there was natural variability in the results. NCPTT staff
evaluated color change and visual appearance between April 2006 and November 2006,
representing changes from six months to twelve months after cleaning. Most changes in
appearance during this time were subtle.
Changes in color measurements were calculated from CIElab coordinates as !L*
(changes in lightness or darkness), Δa* (changes towards red or green), Δb* (changes
towards blue or yellow), and ΔE (total Color change). These results are reported in
Appendix B, Color Measurements on Field Trials.
Further evaluation of the data focused on establishing color change trends by counting
the frequency of color changes at ΔE greater than 5, and ΔE greater than 10. Again, any
changes of color observed were subtle to the human eye. Researchers looked at
frequency trends compared by cemetery, by cleaners, and by sunny or shady location.
The results are reported in Appendix C, Color Analyses by Cemetery, Test Patch,
and Location. Once the frequency tables were created, photographs of each headstone
were carefully examined to determine if measured color changes could be observed in the
photographs. Two important points should be noted about the data. First, additional data
regarding color changes will be measured in forthcoming field trips, thus data for some
headstones continues to be collected. Second, some data from Bath National Cemetery is
missing. These analyses exclude data from Bath National Cemetery at this time.
By looking at the frequency of ΔE color changes, researchers were able to initially
identify headstones that displayed some subtle appearance changes. For example, data
from headstones in Jefferson Barracks is shown in Table 6.
Table 6. Frequency of color change greater than 5 (in yellow) and color change greater than 10 (in
gold) for headstones at Jefferson Barracks National Cemetery, St. Louis, Mo.
By looking at this data, headstones 72 1273 and 72 1370 were identified as displaying
color changes from April 2006 to November 2006. The same analyses were undertaken
for data found in Appendix C from each cemetery. Based on color measurement changes
headstones at Jefferson Barracks displayed the most occurrences of color change in patch
6 (Kodak Photo-Flo). Next, researchers closely inspected photographs of headstones that
displayed color changes to see if further visual changes could be noted. For example,
upon closer inspection of headstone 72-1273, biological re-growth was noted in patch 4
(H2Orange Cleaner) along the inset center cross, see Figure 6. Further review of the
color measurement data indicated that the stone had darkened slightly (based on negative
ΔL* values for all patches).
Figure 6. Close-up detail of headstone 72 1273, showing
signs of biological growth on inset.
On closer inspection of headstone 72-1370 in Jefferson Barracks, scientists noted a
mottling appearance that could be seen in most patches, see Figure 7. The headstone is
darkening. There may be biological re-growth associated with the veining seen in the
stone.
Similar observations can be made at other cemeteries. For example, color change was
noted in several headstones in San Francisco, including WS 1032 B shown in Figure 8.
Based on color measurements, five of the six test patches have changed color by !E
greater that 5. Most of this color change comes from the darkening of the headstone
(negative ΔL* values). Visual observation supports these measurements. Biological
growth can be seen on patch 2 (D2 cleaner) patch 4 (H2Orange cleaner) and patch 5
(WEG marble cleaner). Also, the brown staining seen on the lower portion of this stone
is frequently found in the cemetery. Researchers hypothesize that the staining is due to
the use of iron fortified fertilizer used by contractors in San Francisco National Cemetery.
Next, frequency data of ΔE color change was analyzed by cleaner, see Appendix C. The
frequency of color change is given in Table 7.
Table 7. This table shows the number of color changes greater than 5 and greater than 10 for each
cleaner found on headstones at Alexandria, Jefferson Barracks, San Francisco, and Santa Fe
National Cemeteries.
From this data, Kodak Photo-flo exhibited the greatest number of color changes both
greater than 5 and 10. Based on this frequency analysis, the worst performer was likely
Kodak Photo-Flo. Although Photo-flo test patches, location #6 (Illustration 2), were
lower on the headstones it is unlikely that these changes were a result of rain water
backsplash since water, in adjacent location #3, did not show the same frequency trend.
Finally, frequency data of ΔE color change was analyzed based on the location of the
headstone in sunny or shady locations within the cemetery. The frequency analysis of this
data is given in Table 8. The frequency of color changes greater than 5 is equal in sunny
and shady locations (n = 22), indicating that there is a equal chance of seeing a color
change in a sunny location or a shady location on the headstones. However, there is a
greater chance of seeing a color change greater than 10 in a shady location than in a
sunny location. Fungi and algae tend to grow in shady locations and may lead to greater
visual appearance changes.
Table 8. This table shows the number of color changes greater than 5 and greater than 10
headstones in sunny locations and shady locations at Alexandria, Jefferson Barracks, San Francisco,
and Santa Fe National Cemeteries.
Some unusual visual observations were made at Jefferson Barracks National Cemetery.
It was at this cemetery that Church inadvertently cleaned more stones than were needed
for the study. In follow-up visits, biological activity was observed on these headstones as
well as headstones included in the study. Eight headstones were cleaned at Jefferson
Barracks in October 2005 ñ six headstones were in the shade and two headstones were in
the sun. On all shady headstones, the reoccurrence of biological growth was seen
predominantly on patches cleaned with H2Orange Cleaner (#4). The re-growth was
sometimes seen on other patches #5 and #6 below the H2Orange Cleaner. Figure 9
shows examples of biological re-growth on four of the stones. Sample and swabs and
biological analysis did not indicate any significant differences between patch 4, cleaned
with H2Orange cleaner, and other test patches. Interestingly, six months after these
photographs were taken the dark biological growth had disappeared on all samples! It
may be possible that H2Orange cleaner did not kill all microbes initially, and it took some
time for all growth to die. Alternately, the growth seen on these headstones was seasonal
and may return again in the future. In any case, the reoccurrence of microbial activity left
an undesirable surface appearance for a period of time, thus NCPTT staff recommended
the exclusion of H2Orange cleaner from Phase Two of the study.
Figure 9. Overview and detail photographs of four headstones found in shady locations of Jefferson
Barracks National Cemetery are shown. Microbial activity is found predominantly on patches
cleaned with H2Orange cleaner.Orange cleaner.