6.1. Appearance
Appearance changes of field trails were documented using photography and colorimetry
throughout phase one of the study. Very subtle changes were seen on stones over time
from six months to twelve months after cleaning. However these changes were often not
noticeable to the viewer. None of the cleaners left obvious changes, such as yellowing,
etc., from possible cleaning residues.
Color change trends were examined by determining the frequency of color changes at ΔE
greater than 5 and ΔE greater than 10. Trends were evaluated by cemetery, by cleaners,
and by sunny or shady locations. In most cases where color change occurred, headstones
were darkening.
From frequency trend data associated with cleaners, Kodak Photo-Flo exhibited the
greatest number of color changes greater than 5 ΔE and greater than 10 ΔE, and was
likely the worst performer of the test cleaners. None of the other cleaners were readily
distinguished based on changes in visual appearance.
It is important to note that, while H2Orange cleaner seemed to perform well based on
color measurements, significant visual changes were noted over a six month time period.
The appearance of biological re-growth or staining was not always captured by color
measurements, since changes often occurred at the outer edges of the headstone.
Moreover, after twelve months, the visual changes had disappeared. Despite the fact that
this phenomena was observed at only one cemetery, Jefferson Barracks National
Cemetery, it was deemed to be an unacceptable short term appearance change.
Appearance changes were subtle during the six and twelve month time period. In
general, more time is needed to see significant appearance changes to the headstones.
6.2. Biological Re-growth
Determination of biological re-growth in this study has offered some complex problems,
from the sheer numbers of samples to be evaluated and enumerated, to how cleaning
history of the stones affect the initial biological activity, to the length of time needed for
observing visual biological re-growth.
Biological swabs were taken from many headstones and required considerable time and
effort to enumerate in the course of this study. Initial estimates of the number of samples
to be examined were 7,880 biological counts, taking over 63,000 hours of work to
perform! This was an impossible task and in June 2005, we revised the number of
samples to 600 swabs. Still the task was daunting and ultimately, fewer samples were
evaluated.
All headstones started with a relatively small biofilm of bacteria and fungi at the
beginning of the study, with the exception of headstones located in Santa Fe National
Cemetery which displayed a larger biofilm. This is likely due to the fact that Santa Fe
headstones are not regularly cleaned in the same manner as those located in the other test
cemeteries. Importantly, no algaes or photosynthetic bacteria were observed in the
samples. According to Dr. Ralph Mitchell,20 it is likely that algaes or photosynthetic
bacteria are the greatest source of visual appearance change found on headstones and thus
are the most important to enumerate. Fungi are also sources of visual discoloration, but
to a lesser extent.
As of November and December 2006, no algae were detected in samples from any of the
five cemeteries sampled. Green coloration in some samples was due to the presence of
fungi. Fungi and bacteria were enumerated by plating on solid media and counting
colonies after incubation. Numbers of bacteria and fungi in samples were variable.
The absence of algae or photosynthetic bacteria is significant. These organisms
typically provide the most visual evidence of growth on headstones. Their absence,
even from the stones treated with water, suggests it is still too early to determine the
effectiveness of the biocides.
NCPTT staff attempted to identify performance trends based on the biological activity
documented over the course of twelve months. Performance of each cleaner was ranked
based on data from swabs. Rankings from June 2006 results appeared to illuminate
differences to a greater extent than rankings from February 2007. This is partly due to
the fact that there were six cleaners to rank in June 2006 where as there were four
cleaners to rank in February 2007. The latter rankings grouped more closely together
thus making it more difficult to see significant differences.
Based on the June 2006 rankings, Kodak Photo-Flo was likely the worst performer of the
six cleaners evaluated.
6.3. Physical Changes
Evaluation of physical changes is a significant task in phase 2 of the study. Physical
changes will be evaluated for field test stones and for accelerated weathering laboratory
samples. To date, NCPTT staff has identified methods to be used in evaluating physical
changes to the stones. They include changes in appearance by colorimetry, changes in
surface texture to be monitored by laser profilometry, and changes in porosity to be
examined by mercury porosimetry and Nitrogen BET absorption porosimetry.
Laboratory samples were examined using colorimetry, laser profilometry, and weight
measurements prior to any accelerated weathering studies as the baseline data. Field test
stones will be compared to control samples kept in pristine conditions in the laboratory.
This work is on-going.
6.4. Chemical Changes
As with the evaluation of physical changes, chemical changes caused by cleaners will be
evaluated in the laboratory as part of phase 2 of the study. The possible presence of
soluble salts will be evaluated using optical microscopy and analysis of total soluble salts
using both gravimetric and conductivity methods. The chemical nature of the
efflorescence may be studied using X-ray Diffraction analysis. Detection of possible
cleaning residues or minor chemical changes may be studied using Electron Microscopy-
EDS, and X-ray Fluorescence Spectroscopy.
NCPTT staff has tested its new portable XRF analyzer for identifying chlorides on field
test stones with success. The task of identifying chemical changes to the stones
continues.
20 Mitchell, Ralph. Harvard University, Division of Engineering and Applied Sciences, personal
communication, March 2007.