The first accelerated weathering study began on July 24, 2006. This study was conducted
by Georgette Lang, a chemistry major at Centenary College of Shreveport, Louisiana
under the supervision of Jason Church. For this study two types of marble were cored and
prepared. Three replicate samples of marble were prepared for each type of cleaner.
Along with these samples, three untreated samples of each marble type were readied as
internal standards. Finally, three samples of each marble were prepared that would not be
treated in the Weatherometer but remained untreated as control samples. This brought the
total number to 48 samples. Each sample was given a unique number which encoded
information about marble type, chemical cleaner used and the sample identification
number. This unique 3 digit number was inscribed on the back of each sample.
Pre-existing conditions of the marble surface were recorded by using the Laser
Profilometer (see section 4.3.2.1.1.) to map the surface of each sample prior to treatment.
Each sample was photographed and color measurements were taken to check for any
color change as a result of the application of the cleaners. The weight of each sample was
recorded as a baseline to identify residual material deposited from the cleaning. Once the
samples were documented and mounted into the Weatherometer sample holders, the 800
hour test was initiated.
The samples were sprayed with the select cleaner and rotated inside the Weatherometer
on a daily bases. The marble was treated with the six cleaners D2, Daybreak, Kodak
Photo-flo, H2Orange2, Marble Cleaner, and water (plus one set that was weathered but
untreated). Each of the chemicals was mixed to the manufactures recommendation and
applied to the sample using a 16 oz hand pump spray bottle. The samples were removed
from the Weatherometer in their holder and sprayed to completely wet the surface at the
end of a dark cycle at approximately the same time each day. The end of a dark cycle was
chosen as a time for treatment so that the cleaner would have sufficient time to soak into
the stone without evaporating at elevated temperatures during the UV exposure. After the
sample was sprayed, it was placed back into the Weatherometer without being rinsed.
The decision was made not to rinse the marble after it had been treated because 4 out of
the 5 cemeteries involved in the study stated that they do not rinse their stones post
cleaning.
On August 27, 2006 the Weatherometer run ended and the samples were left in the
powered down Weatherometer for 48 hours to allow any moisture in the stone to
evaporate. Testing began after the samples were removed from their holders. Once
accelerated weathering was concluded, testing repeated using the same methods as pretesting
documentation. First, the weight measurement is taken. Second, samples were
photographed, and third, colorimetry measurements were taken. Finally, surface texture
on each sample was measured using the laser profilometry. Also, at this time each of the
elemental composition of sample surfaces were analyzed using the Tracer III portable XRay
Fluorescence Spectrometer. The XRF Spectrometer under the following conditions:
to the Rhodium target Xray tube was set to 15kv and 15ma. A vacuum pack was
connected to the Spectrometer and a vacuum of 2 torr was pulled. All spectra were
collected for 180 seconds. Spectra were taken of the front and the back surface of
samples from both marble types treated with each cleaner. This helped to determine if
any chemical residue had migrated through the sample.
Figure 12. Jason Church uses the XRF spectrometer to analysis a marble sample after artificial
weathering.
There were a variety of results from the first accelerated weathering test. Colorado Yule
marble was more likely than Cherokee White marble to display deterioration or
discoloration in the accelerated weathering test. NCPTT is currently looking into the
possible reasons that the Colorado Yule marble samples were affected at a greater rate
than the Cherokee White marble samples.
There was no discernable change in the samples that were untreated or treated with water.
The Colorado Yule marble samples treated with D/2 discolored and took on a slightly
translucent appearance. The backs of the Colorado Yule samples also had a very fine
powdery deposit on them. When the backside of one sample was examined with the XRF
there was a slight Potassium peak. The Colorado Yule samples that were treated with
Daybreak discolored to a yellow appearance and had a fine ìsandyî coating on the
backside. When the backside of one Colorado sample was examined with the XRF a
large Chloride peak was detected. The remaining 3 cleaners (Photo-Flo, WEG Marble
Cleaner and H2Orange2) had no obvious detectable deterioration.
The thirty three day study represents a worst case scenario where the marble was
saturated with a cleaner on a regular base and was not rinsed after cleaning. Any physical
change to the marble or chemical deposition on the marble would likely be scene in an
extreme situation. Because of the severity represented in the first accelerated weathering
study the decision was made to start a second accelerated weathering study.
5.1.1.2. Four Time Cleaning Study
The second accelerated cleaning study used the Q- Panel Lab Products model QUV/
Spray Accelerated Weather Tester preformed at NCPTT began on December 22, 2006
and ended its 800 hour cycle on January 19, 2007. The second accelerated weathering test
was an abbreviated version of the first experiment. For the second study only Colorado
Yule marble was selected for testing. This decision was made due to the fact that
deterioration was evident on the Colorado marble in the first experiment. These samples
were prepared from the same marble using the same procedure as in the first accelerated
weathering experiment.
For the second experiment only 10 samples were prepared for Weatherometer exposure.
These consisted of 2 Colorado Marble replicates for each cleaner. Each sample was
sprayed with D/2, Daybreak, WEG Marble Cleaner, or water. Two cleaners, H2Orange
Cleaner and Kodak photo-Flo, were removed excluded from the accelerated weathering,
based on results of phase one of the study. Two untreated samples were weathered in this
experiment as internal controls. Each of these samples was given a unique 3 digit
number that was inscribed on the back of the stone.
One key feature of this study was the decision to only clean the samples weekly, once at
the beginning and then three more times at the same cycle on each following Friday. This
cleaning schedule may have provided a more realistic approach to the accelerated
weathering. Also in this study, the cleaner was sprayed onto the sample then rinsed
shortly after being treated according to manufacturersí suggested cleaning directions.
After the 800 hours of weathering was completed, the samples were analyzed in the same
steps as the first experiment including laser profilometry and colorimetry. A few
additional tests were added to this study to try and get a more detailed view of the stones
reaction to the cleaner. Salt deposits were visible on both the back side of some samples
and on the Teflon Weatherometer holder ring that surrounds the stone in place.
Gravimetric measurements were taken of each of the stone samples while they were still
in the holder. Crystalline grow was visible on the backside of the samples treated with
both D/2 and Daybreak.
In addition to the usual photo documentation the samples were also photographed under
magnification using both a Leica MZ8 boom microscope at a magnification range of 10x
to 50x and a Leica DMRX polarized light microscope at a magnification range of 100x to
500x. Both microscopes were fitted with a Diagnostic Instruments Inc. Digital Spot
Camera. Through this process the shape, appearance, growth pattern and relative size of
the crystalline growth can be documented.
Figure 13. Examples of salt formation on marble samples treated with D/2 (left) and Daybreak
(right) both viewed under 100x magnification.
Future research activities will investigate the chemical composition of the efflorescence
found on the samples. Both the face and back of all of the samples will be analyzed
using the portable XRF Spectrometer. Samples of the salt will be analyzed using X-ray
Diffractometry. This will help to determine the bases of the visible salts and any other
type of detectable chemical residue left on the stone after cleaning.
Treated and weathered Colorado Yule samples are still being tested and the data
processed at this time. New testing methods are currently being considered to maximize
the identification of the salt contents in the samples and to identify any other chemical or
physical changes that may have taken place in the samples as a result of the cleanerís
application.