Post on 13-May-2023
Journal of the American Ceramic Society 94(8)(2011)2585-2591.
Rehydration/Rehydroxylation Kinetics of Reheated XIX-Century
Davenport (Utah) Ceramic
Patrick K. Bowen1†, Helen J. Ranck1, Timothy J. Scarlett2, and Jaroslaw W. Drelich1
1 Department of Materials Science and Engineering
2 Department of Social Sciences
Michigan Technological University, Houghton, MI 49931
Abstract
Rehydroxylation Dating (RHX dating) has recently been proposed as a new chronometric
dating tool for use on archaeological fired-clay ceramics. The technique relies upon the well-
known characteristic of reheated porous ceramic vessels to regain water, the kinetics of which
has been shown to follow a (time)1/4 power law at temperatures of 13-50°C . In this study,
experiments were conducted in which the mass measurements taken from 19th-century ceramic
artifacts revealed a deviation from the (time)1/4 power law over a wide range of temperatures.
This finding has led to the formulation of an empirical equation which describes the observed
ceramic’s rehydration and rehydroxylation behavior as an additive process in which the long-
term mass gain is dictated by a (time)1/n power law. As part of this study, the mineralogy of the
ceramics and their thermal properties have been evaluated. The instantaneous effect of humidity
on mass measurements was demonstrated to be the principal source of error.
Financial support for this study was provided by the Charles and Carroll McArthur Research
Internship program, the Michigan Space Grant Consortium undergraduate fellowship, and the
Summer Undergraduate Research Fellowship at Michigan Technological University.
†Author to whom correspondence should be directed. e-mail: pkbowen@mtu.edu
1. Introduction
Archaeologists currently have only a limited number of techniques with which to date
ceramic artifacts including thermoluminescence dating, archaeomagnetic dating, relative dating
through use of superposition and association, analyzing stylistic elements, and, in limited cases,
carbon-14 (radiocarbon) dating of associated organic residues. The only lab techniques
applicable to most pottery sherds and archaeological ceramics are thermoluminescence and
archaeomagnetic dating. Both techniques require advanced analytical tools, trained personnel,
and therefore are expensive and not affordable to every archeological laboratory.
Recently, Wilson et al. proposed a new, simple chronometric dating technique called
fired-clay Ceramic Rehydroxylation Dating (RHX dating).1 It relies on monitoring the mass gain
of reheated porous clay objects exposed to water vapor. This low-cost technique, if it can be
successfully applied to archaeological samples, offers significant advantages over many
established ceramic dating techniques. Therefore, it is crucial that the kinetics for fired-clay
ceramics to regain water be well understood. Questions remain regarding the effects of
mineralogy, humidity, and temperature on water absorption behavior. It is the purpose of this
study to address some of these questions.
1.1. Rehydroxylation Dating
Wilson et al. observed that fired clay objects quickly regain waters of hydration and
slowly undergo rehydroxylation process in a manner that follows a (time)1/4 power law.2,3,4
Waters of hydration are physically bonded—water that is adsorbed as well as that which causes
clay interlayer swelling—while hydroxyl water is returned to the clay mineral during
reconstruction after firing in the form of structural OH groups.
3
Wilson’s research team determined that the rate of mass gain and volume expansion for
fired-clay ceramic artifacts was governed by a (time)1/4 power law,1-4 described by Equation 1:
m(t) = γt14 + δ (Eq. 1)
The constant "γ" was previously called the "Rehydroxylation Rate Constant." Equation
1 also accounts for some initial mass after firing, "δ." This 1/4 power law was evident when
examining the long-term mass increase of samples at a constant temperature in the range 13-
50°C.
Using the (time)1/4 power law in conjunction with an artifact’s measured mass gain
behavior (mass gain since the sample was last fired) and the mean lifetime temperature, one is
able to calculate a calendar date for manufacture. Wilson’s team published accurate dating
results on ceramic fragments ranging in age from approximately 200 days to nearly 2000 years.
They argue that the dating technique should work over millennial timescales.
Temperature is the sole significant factor influencing the rate of water absorption by
heated porous ceramic vessels. In the initial study, the authors derived a mean temperature
calculated from temperature records from several stations in southern England.5 Wilson’s team
expressed their concern about the uncertainty that unknown temperature variations produced in
their age calculations.
1.2. Effect of Mineralogy
When fired to sufficient temperatures many clay minerals, such as illite, undergo
reversible dehydration and dehydroxylation along with other reversible and irreversible physical
and chemical changes.6,7 Other clay minerals, such as kaolinite, undergo irreversible
dehydroxylation at different temperatures as they vitrify and enter an amorphous glass phase.8
Throughout the process of firing, ceramic samples undergo chaotic, uneven changes along the
4
entire thermal cycle, particularly for pottery (fired at low temperatures, < 900°C) and ceramic
(fired at higher temperatures, < 1200°C) artifacts that include building materials like brick and
tile. The conversion of crystalline clay minerals into anhydrous materials is rarely complete,
however. Wilson et al.1 suggest that RHX dating could be used on ceramic materials with a
wide range of chemical compositions and crystalline structures produced using a wide range of
firing temperatures.
Because RHX dating procedures require measuring each sample's characteristic
rehydroxylation behavior, the technique requires no comparative standardization or
foreknowledge of the sample’s mineralogy. Wilson et al. noted that the complexities of
molecular- and nano-scale processes of diffusion that govern rehydroxylation are not fully
understood. Because of the self-calibrating nature of the technique, the unknown nanoscale
processes should not hinder the application of RHX dating.
1.3. Goal of This Study
In this study, a general equation that describes rehydration/rehydroxylation behavior of
archaeological ceramics is developed and its dependence on temperature analyzed. The impact
of humidity on instantaneous mass measurements is also addressed. The Davenport ceramic is
characterized both structurally and thermally in this study in order to identify the temperature at
which the sample experiences dehydroxylation and attempt to relate it to its constituent clays.
2. Materials and Methods
2.1. Pottery Samples
Samples for this study came from an excavation at the site of a 19th century pottery shop
owned by the Davenport family, located in the Parowan valley in Utah. The samples obtained
from this fieldwork presented an ideal opportunity to apply RHX dating because the archaeology
5
team had extraordinary chronological control of the site’s features and stratigraphic deposits.
The chronology was exclusively relative, however. The development of a refined expression for
rehydration/rehydroxylation behavior would allow a dramatic enhancement of the
anthropological research questions currently being posed at the site.9-12
Ceramic sherds were recovered from numerous stratigraphic levels at the excavation site.
They were then washed with tap water and soft-bristle brushes to remove debris, dried, and
stored in an open-air container. A large (>200 g) sample was selected and broken apart into
smaller, individual pieces. Fragments of pottery selected for the rehydration study each weighed
between 32 and 96 g, while other fragments were used in various analyses to characterize the
ceramic. Table 1 shows the fragments of the large sample and their uses. Note that four of the
samples were used in rehydration/rehydroxylation experimentation.
The mass of sample 1 was close to capacity of the balance, so it was used only for a
single trial due to concerns about the accuracy of the balance when it was loaded close to
capacity. Samples 2-4 were smaller, and they were used repeatedly in order to ensure that all of
the samples had been fired at the same temperature, were precisely the same age, and had
uniform mineralogy.
2.2. X-Ray Diffraction Analysis
A sample was prepared from a fragment of pottery which was ground in an agate mortar
until fine. X-ray diffraction (XRD) experimentation was performed using a XDS-2000 (Scintag
Inc., Cupertino, California) diffractometer with a copper target (λKα = 1.540562 Å) and a
graphite monochromator. The scans were performed continuously from 10o to 85o in 2θ at a
speed of 0.2o per minute with a step size of 0.03o. The XRD instrument was run with a potential
difference of 45 kV and a current of 35 mA. The divergence slit widths were 1 mm and 2 mm
6
and the receiving slits were 0.3 mm and 0.5 mm. Peaks on the collected spectrum were
identified by using the DMSNT (Scintag, Inc.) software package in tandem with the Powder
Diffraction Database Search (PDDS) software (Scintag, Inc. and Radicon, Ltd.). The PDDS
software was used to search the Joint Committee on Powder Diffraction Standards-International
Center for Diffraction Data (JCPDS-ICDD) database. The spectrum was smoothed by using a
10-point average, in an attempt to minimize the appearance of background noise.
2.3. Thermogravimetric Analysis
The thermogravimetric analysis (TGA) / differential thermogravimetric analysis (DTGA)
were performed using a Q600 (TA Instruments, New Castle, Delaware) instrument equipped
with simultaneous DSC/TGA capabilities. The instrument was evacuated and purged with
nitrogen gas before the experiment began, and the gas was circulated through the instrument at
100mL/min during the experiment. The samples were placed in alumina pans contained inside
the TGA instrument. Data was collected from room temperature up to 750oC at the rate of
2oC/min.
2.4. Drying and Re-Hydration Procedures
Removal of physically bonded absorbed water (dehydration) was carried out in the dryer
at approximately 110oC until the mass of ceramics sample had stabilized, typically after 20-30
hours. The samples were weighed using an Ohaus (Pine Brook, NJ) Adventurer AR2140
balance with 0.1 mg precision, and then placed in the furnace at 500 oC (sample 1) or 650oC
(samples 2-4) to remove chemically bonded water (dehydroxylation) for 4 (sample 1) to 12 hours
(samples 2-4). The samples were removed from the furnace after dehydroxylation, stored in the
desicator, and weighed soon after the samples had cooled to room temperature.
7
The freshly dehydrated/dehydroxylated and massed samples were placed on glass Petri
dishes and exposed to air with a relative humidity of 20-28% in either: ambient laboratory
conditions (22±2oC), a drier (~80oC), or a refrigerator (low temperature between -2 and 3oC).
Both temperature and relative humidity were continuously monitored using an indoor La Crosse
(La Crosse, WI) unit (model WS-9410TWC) with temperature and humidity precisions of 0.1oC
and 0.6%RH, respectively. Temperatures and relative humidities used in rehydroxylation
experimentation are listed in Table 2 along with their standard deviations.
The samples stored in the room temperature environment were covered to prevent the
deposition of dust. Elevation of the cover allowed laboratory air to circulate freely around the
samples to maintain a constant humidity level. In selected experiments the samples remained
inside the balance for the entire time that their masses were being monitored. In these
experiments, the top cover of the balance remained closed, but the side doors were opened
slightly to allow free circulation of air. The weight of samples during their exposure to ambient
laboratory conditions was typically monitored for two to three weeks.
2.5. Statistical Analysis
Because analysis of the data required fitting it to a complicated, non-linear function, the
MATLAB nlinfit function was utilized. This function utilizes the Levenberg-Marquardt
algorithm13 to generate a non-robust, least-squares functional fit to the data. A 95% confidence
interval was generated for all of the fit parameters by using the nlparci function in conjunction
with the Jacobian matrix generated by the nlinfit function. Some data sets held at room
temperature experienced large, systematic humidity fluctuations which skewed the data in such a
way that a fit could not be performed. Note that no individual data points were eliminated during
this analysis; hence all of the data sets used in this study were analyzed in their entirety.
8
Verification of a linear relationship (a relationship with a nonzero slope) was performed
by using a two-tailed test for significance. In this test, the t-distribution was utilized, and the null
hypothesis was slope equal to zero (standard for a linear significance test). The resulting t-
statistic was then correlated to the appropriate p-value to obtain the fit significance. All
calculations of standard deviation were done in the style of a sample standard deviation, "s," (as
opposed to a population standard deviation, "σ").
3. Results and Discussion
3.1. Mineralogical Study of Davenport Pottery
X-ray diffraction analysis performed on the pottery revealed a complex spectrum,
presented in Figure 1, which is composed of many phases. Extremely large peaks were observed
at 20.9o and 26.6o. These were attributed primarily to large amount of quartz present in the
pottery sample. Interestingly, a comparison of the Parowan Valley clay deposits by Watkins14
indicated that the maximum quartz content of most raw clays in the region is 20-30%. The large
amount of quartz is likely due to either the addition of sand temper, used to change the thermal
properties of the clay15 or a byproduct of the washing/settling process used to prepare the raw
clay for use. Watkins also indicated that many Parowan Valley clay formations contain a large
(>50%) amount of plagioclase (soda-lime) feldspar. From this description, it was probable that
high-concentration anorthite (ICDD-JCPDS No. 89-1462) and low-concentration albite (84-
0752), the end compositions of plagioclase feldspars,16 could be identified. Their presence is
confirmed by the presence of characteristic peaks at 21.9o, 22.0o, and 28.0o.
After verifying the presence of plagioclase feldspar(s) and quartz , an intensified
literature search yielded a significant amount of information about other possible constituents.
High-feldspar formations in the Parowan valley were likely to contain biotite, hornblende,
9
sanidine, pyroxene, and miscellaneous Fe/Ti oxides.17,18 Sanidine (77-0981) was readily
identifiable, given the high visibility of characteristic peaks at 29.8o, 27.0o, and peak asymmetry
present at 21.0o. Biotite (88-2192) was identified by the presence of small peaks at 34.1o and
41.5o. The small size of the peaks indicates that the amount of biotite is likely close to the
detection limit of the XRD instrument, which is typically on the order of 0.5%.19 The iron and
titanium oxides, hematite (87-1166) and rutile (87-0710), respectively, were also identified in
roughly the same quantity as biotite, as approximated by their characteristic peak heights.
Mullite (83-1881), an aluminum silicate, was identified by the presence of a small characteristic
peak at 16.5o. The other common constituents, hornblende and pyroxene, did not appear to be
present in this sample.
The common minerals calcite (5-586) and diopside (11-654) are also present in this
spectrum, as evidenced by the composite peak at 29.7o, the strong diopside peak at 31.3o, and the
calcite peaks at 39.3o and 43.0o. The occurrence of calcite in fired-clay pottery could be
explained by either (i) gradual weathering processes that transform dehydrated, partially
decomposed anorthite into calcite or (ii) recarbonation of calcite that was decarbonated during
the original firing process.20 Diopside was likely evolved in a complex series of mineralogical
transformations that take place at temperatures ranging from 900oC to 1100oC, as shown in the
study by Trindade et al.21
Watkins indicated that one particular clay deposit, described as "the Bauers Tuff Member
of the Condor Canyon Formation," located in the southwestern part of the Parowan Valley,
contains plagioclase feldspar (55%), sanidine (35%), biotite (7%), iron/titanium oxides (3%), and
a trace amount of pyroxene.14 This clay formation could be the one from which this pottery was
manufactured.
10
A qualitative identification of lower volume fraction clay minerals is difficult due to the
XRD detection limit, however it appears as if one minor constituent could be illite (35-0652), as
indicated by the presence of a peak at 25.7o and another, smaller, peak at 17.3o. Another possible
minor constituent is metahalloysite (74-1023), the dehydrated companion of halloysite,22 as
determined by the small peak at 20.1o and the size of the composite peak at 24.0o. This
particular meta-clay is quite rare, and the identification is tentative at best as there is no concrete
evidence that the source clay contained halloysite. Given the small amount of clay present in
these samples relative to non-hydrating or amorphous material, it is reasonable to conclude, as
Wilson et al. did, that the maximum expected mass gain over the lifetime of such a sample
would not exceed 1-2%.
3.2. Thermal Study of Davenport Pottery
The TGA and DTGA curves from a sample of Davenport pottery are presented in Figure
2. There appear to be two, distinct regions in this curve. The first is a slow, relatively constant
loss of mass that begins just after 27°C and continues to about 540°C. This loss in mass can
likely be attributed to the loss of capillary water and physically bonded water in the sample, as
well as a small amount of dehydroxylation. The major loss of mass occurs at approximately
642°C as determined by the minimum in the DTGA curve.
At 642°C, it is assumed that all of the weakly-bonded water has been removed, and the
remaining mass loss occurs as the hydroxyl water escapes from the clay minerals. This result
agrees well with the location of the second stage of mass loss peaks in several studies utilizing
TGA23 and differential thermal analysis (DTA).24,25 The DTA study of clays by Grim and
Bradley25 indicates that when many types of clays (including calcareous montmorillonites, some
illites, and many kaolinites) are fired and left to age for a period weeks (or sometimes months),
11
the shape of the DTA/TGA takes on a form similar to what was observed in this
experimentation. In other words, the only significant thermal activity is observed at
temperatures around 700°C. It should be noted that decarbonation of calcite in the sample could
contribute to the sharp drop at ~642°C, although the results of Grim and Bradley point to mass
loss dominated by the escape of hydroxyl water.26,27
It is difficult to determine exactly which clay causes this type of thermal behavior. The
dehydroxylation temperature of 642°C could be due to the presence unfired halloysite, kaolinite,
pyrophyllite, or any number of montmorillonites.25 Additionally, a significant shift in
dehydroxylation temperature is often observed after clays are fired for the first time and left to
age,27 so this particular temperature may not be representative of the raw material.
The 500oC temperature used by Wilson et al. would not be sufficient to completely
dehydroxylate the samples used in this study, so a higher firing temperature was required.
Calcite, when heated to high temperatures, tends to decompose to calcium oxide by releasing
carbon dioxide. Thus, care was taken to ensure that the selected dehydroxylation temperature
would minimize decomposition. After careful consideration, a dehydroxylation temperature of
650oC was selected to precede the rehydration/rehydroxylation experimentation.
Slow dehydration/dehydroxylation behavior was observed over the course of about 2.5
weeks at a temperature just above the boiling point of water (105°C). Samples 2, 3, and 4 were
placed in the dryer prior to firing in experiment 2, and the resulting set of normalized mass-loss
data is presented in Figure 3. These data show remarkable consistency, even between samples
of very different masses. The power-law fit analysis of these data yields an average power of
0.102 ± 0.005 (95% confidence).
3.3. An Empirical Model for Rehydration/Rehydroxylation Behavior
12
Rehydration/rehydroxylation behavior was observed to be similar to that presented by
Wilson et al.1 Mass gain curves for a sample held at a low temperature as well as one held at
room temperature are presented in Figure 4. The fractional mass gain of the low temperature
sample (sample 2 from experiment 4) at 250 hours is ~0.4%. In comparison, the fractional mass
gain of the room temperature sample (sample 4 from experiment 3) is ~0.6%; an increase of
50%. The drastic increase in mass gain from low to room temperature indicates that there is a
certain temperature dependence. This temperature dependence was explained by Wilson et al.1
to be thermally activated in the temperature range of 13-50°C, but this study failed to reproduce
those findings at different temperatures.
These mass gain curves in Figure 4 represent neither solely rehydroxylation (described by
the power law of Wilson et al.) nor rehydration behavior, but rather a combination of the two.
Rehydration/rehydroxylation of a ceramic sample, after it is removed from the furnace, consists
of two, distinct steps.3,4 The first event is fast penetration by atmospheric water vapor, which
adsorbs onto the surface of the pores and meta-clay, and ultimately causes the clays present in
the sample to swell. At the nanoscale, swelling behavior is caused by the diffusion of between
one and four molecular layers of water into the interlayer spacings between the clay sheets.28,29
After liquid water penetrates the sheets of the clay minerals, the chemical recombination
(rehydroxylation) begins to take place. The interlayer water in the clay sheets slowly begins to
diffuse into the nano-scale pores within the clay sheets, with diffusion likely falling into either a
Knudsen30 regime, a single-file31 regime, an anomalous diffusion (subdiffusion) regime,32 or
some combination thereof. It is unlikely that traditional (Fickian) diffusion33 would take place at
these small scales.
13
Thus, any complete empirical model attempting to quantify mass gain behavior must
consider both the short-term mass gain caused by interlayer swelling and the long-term mass
gain presumably caused by rehydroxylation. It was found through careful analysis that the initial
rehydration behavior is described rather well by the integral form of the Lagergren rate
equation.34 Use of this particular function gives the beginning of the mass gain curve the form of
inverted exponential decay. The long-range term was constructed such that the power associated
with it is treated as a fitting parameter, and therefore has not been constrained to 1/4.
The resulting expanded empirical model for rehydration/rehydroxylation is presented as
Equation 2:
m(t, T, H) = β(H)(1 − exp(−αt)) + γt1
n(T) + δ (Eq. 2)
This equation has five constants (four if considering normalized mass values, as δ=0) and
three independent variables, although two are considered to be constant during the fitting
process. The constants are defined as: α (hr-1), a kinetics constant for the Lagergren rate
equation term, β (g), a scaling factor for the first term which varies directly with humidity, γ
(g/hr1/n), which was dubbed the "rehydroxylation rate constant" by Wilson et al. and describes
the magnitude of the rehydroxylation activity, δ (g), the inherent (dehydroxylated) sample mass,
and n, which is a temperature-dependent exponent which describes the kinetics of
rehydroxylation. We will refer to n as the "rehydroxylation exponent" in this discussion.
The additive behavior of this equation is illustrated in Figure 5. Note that for the vast
majority of the data, the first (rehydration) term essentially acts as a constant. However, when
the few data points taken early in the experiment are considered, as in the Figure 5 inset, the first
term provides a rather good fit to the data. This is true of all mass gain data to which we have fit
14
Equation 2 (using nlinfit in MATLAB). The normalized fit parameters resulting from the nlinfit
analyses for all mass gain data are presented in Table 3.
3.4. Temperature and Humidity Dependence of the Empirical Model
From the fit parameters in Table 3, it can be surmised that the values of "n" (the
rehydroxylation exponent) are not constant across all temperatures. When the rehydroxylation
exponent is plotted against temperature, as in Figure 6, a strong, direct relationship becomes
apparent. When a detailed regression analysis is performed on these best-fit n and temperature
data, one can state that a linear (or some similar) correlation exists with confidence greater than
99.9%. The resulting regression line gives n(T) = 0.0386 T - 7.912, where T is the temperature
in Kelvin. This means that, according to the analysis performed, n=4 at 35 ± 2°C (standard
error) which agrees reasonably well with the conclusion drawn by Wilson et al. that n=4 at room
temperature.
This temperature-dependent behavior of the rehydroxylation exponent adds another
dimension to the RHX dating technique. If ceramics (or other fired-clay items) are stored in an
extreme-temperature environment, outside the range of temperatures that have been considered
in other studies, then a variation in "n" could have a large impact on the dating results. In
addition, we wonder about the role played by high pressure in rehydroxylation of ceramics from
underwater archaeological sites, particularly those located in deepwater maritime environments
or those deposited in terrestrial contexts where the average ambient temperature underground
varies considerably from the average atmospheric temperature.
Changes in humidity produced instantaneous fluctuations in the measured mass, and are
demonstrated here to be the principal source of error in mass measurements. This is illustrated
qualitatively by Figure 7, which contains the mass and humidity data collected for sample 2 in
15
experiment 2. When the residual mass values from the latter part of the curve are plotted against
the humidity deviation (departure from the mean humidity value), as in the Figure 7 inset, a
linear relationship is observed. This shows that tight humidity control in the laboratory setting is
absolutely essential for RHX dating to become a viable option for the dating of ceramics.
When a linear regression analysis is performed, a nonzero slope is confirmed with 90%
confidence, which is sufficient for a simple analysis. This analysis gives the fractional mass
change per percent relative humidity to be 4.92x10-5 %RH-1. A linear relationship would imply
that only a first-degree term, such as β, is affected by these humidity fluctuations. Thus, the
error at 95% confidence associated with any instantaneous mass measurement becomes ±1.96s,
where s is the sample standard deviation (if humidity is treated as a nonvariant statistic). In this
case, any measurement can then have an associated deviation in humidity of ±2.74 %RH, or
(using the result from the linear regression) an error in fractional mass of ±1.35x10-4 (about 2.3%
of the total fractional mass gain).
4. Conclusions
The results of this study indicate that temperature, humidity, and mineralogy must all be
taken into account when quantifying the kinetics of rehydration/rehydroxylation. Experimental
results collected from samples that were rehydrated/rehydroxylated over a wide range of
temperatures have shown that the 1/4 power law of Wilson et al. does not accurately describe
rehydroxylation kinetics at temperatures significantly different than room temperature. It has
also been demonstrated that the proposed expanded empirical model for
rehydration/rehydroxylation provides a good fit to data over time periods of up to three weeks.
The effect of humidity on the instantaneous mass of the ceramic sample appears to be
significant. The mass of a typical ceramic sample appears to increase by about 0.005% per 1%
16
increase in relative humidity. Thus, exceptionally precise humidity control must be exercised
when rehydroxylation dating is applied to archaeological ceramics, and any systematic humidity
fluctuations must be accounted for during subsequent error-propagation analyses.
Dehydroxylation is impacted significantly by the sample’s mineralogy, so care must be taken to
select a temperature that will remove all of the hydroxyl water contained in the sample while
maintaining the integrity of all of the other constituents. This can be accomplished by
performing TGA analysis.
Future work will be conducted under tightly controlled humidity and temperature
conditions to assess: (i) the temperature and humidity dependence of the Lagergren kinetics
constant and scaling constant and (ii) the temperature and humidity dependence of the
rehydroxylation rate constant when the power is not fixed at 1/4. After the temperature
dependence of these parameters is quantified, the empirical model presented in this study should
be expanded in order to accommodate a more general description of temperature.
5. References
1M. A. Wilson, M. A. Carter, C. Hall, W. D. Hoff, C. Ince, S. D. Savage, B. McKay, and I. M.
Betts. "Dating fired-clay ceramics using long-term power law rehydroxylation kinetics," Proc. R.
Soc. London, Ser. A, 465 (2108), 2407–2415 (2009).
2M. A. Wilson, W. D. Hoff, C. Hall, B. McKay, and A. Hiley, "Kinetics of moisture expansion in
fired clay ceramics: A time^1/4 law," Phys. Rev. Lett., 90 (12), 1–4 (2003).
3S. D. Savage, M. A. Wilson, M. A. Carter, B. McKay, and W. D. Hoff, "Mass gain due to the
chemical recombination of water in fired clay brick," J. Am. Ceram. Soc., 91 (10), 3396–3398
(2008).
17
4S. D. Savage, M. A. Wilson, M. A. Carter, W. D. Hoff, C. Hall, and B. McKay, “Moisture
expansion and mass gain in fired clay ceramics: a two-stage (time)^1/4 process,” J. Phys. D.:
Appl. Phys., 41, 055402 (2008).
5D. E. Parker, T. P. Legg, and C. K. Folland, "A new daily central England temperature series,"
International Journal of Climatology, 12, 317–342 (1992).
6L. Heller, V. C. Farmer, R. C. Mackenzie, B. D. Mitchell, and H. F. W. Taylor, “The
dehydroxylation and rehydroxylation of trimorphic dioctahedral clay minerals,” Clay Minerals
Bull., 5, 56-72 (1962).
7K. Traore, F. Gridi-Bennadji, and P. Blanchart, “Significance of kinetic theories on the
recrystallization of kaolinite,” Thermochim. Acta, 451, 99-104 (2006).
8W. E. Worrall, Clays and ceramic raw materials, Elsevier Applied Science Publishers, 2nd
edition, 1986.
9J. Montcalm, A Burning Question: Archaeology at the Davenport Pottery and Technological
Adaptation in the Mormon Domain, MS thesis, Michigan Technological University, Houghton,
2010.
10T. J. Scarlett, Potting In Zion: Craft and Industry in Utah, 1848–1930, PhD thesis, Department
of Anthropology, University of Nevada, Reno, 2002.
11T. J. Scarlett, Trade and Exchange: Archaeological Studies from History and Prehistory,
"What if the Local is Exotic and the Imported Mundane? Measuring Ceramic Exchanges in
Mormon Utah," Springer Verlag, New York, NY, 2010.
12T. J. Scarlett, R. J. Speakman, and M. D. Glascock, "Pottery in the Mormon economy: an
historical and archaeometric study," Historical Archaeology, 41 (4), 70–95 (2007).
13G. A. F. Seber and C. J. Wild, Nonlinear Regression, Wiley-Interscience, Hoboken, NJ, 2003.
18
14C. N. Watkins, Parowan pottery and fremont complexity: Late formative ceramic production
and exchange, Master’s thesis, Brigham Young University, 2006.
15A. O. Shepard. Ceramics for the Archaeologist. Carnegie, Washington, D.C., 1985.
16A. N. Winchell, "Studies in the feldspar group," The Journal of Geology, 33 (7), 714–727
(1925).
17J. J. Anderson and P. D. Rowley, "Cenozoic stratigraphy and of southwestern high plateaus of
Utah," Special Paper 160, Geologic Society of America, 1975.
18P. L. Williams, Stratigraphy and petrography of the Quichapa group, southwestern Utah and
southeastern Nevada, PhD Thesis, Unpublished, University of Washington, Seattle, 1967.
19F. H. Chung and D. K. Smith, Industrial applications of X-ray diffraction, CRC Press, 1999.
20S. Shoval, P. Beck, Y. Kirsh, D. Levy, M. Gaft, and E. Yadin, "Rehydroxylation of clay
minerals and hydration in ancient pottery from the ’Land of Geshur’" J. Therm. Anal., 37, 1579–
1592 (1991).
21M. J. Trindade, M. I. Dias, J. Coroado, and F. Rocha, "Mineralogical transformations of
calcareous rich clays with firing: A comparative study between calcite and dolomite rich clays
from Algarve, Portugal," Appl. Clay Sci., 42, 345–355 (2009).
22G. W. Brindley, K. Robinson, and D. M. C. MacEwan, "The clay minerals halloysite and meta-
halloysite," Nature, 157 (3982), 225–226 (1946).
23A. F. Gualtieri and S. Ferrari, "Kinetics of illite dehydroxylation," Phys. Chem. Miner., 33,
490–501, (2006).
24R. E. Grim and R. A. Rowland, "Differential thermal analysis of clay minerals and other
hydrous materials," Am. Mineral., 27 (11,12), 746–761, 801–818 (1942).
19
25R. E. Grim and W. F. Bradley, "Rehydration and dehydration of the clay minerals," Am.
Mineral., 33 (1), 50–59 (1948).
26S. Shoval, “Using FT-IR spectroscopy for study of calcareous ancient ceramics,” Optical
Materials, 24, 117-122 (2003).
27S. Shoval, M. Gaft, P. Beck, and Y. Kirsh, “The thermal behavior of limestone and
monocrystalline calcite tempers during firing and their use in ancient vessels,” J. Therm. Anal.,
40, 263-273 (1993).
28H. vanOlphen, An Introduction to Clay Colloid Chemistry, John Wiley & Sons, 1963.
29E. J. M. Hensen and B. Smit, "Why clays swell," J. Phys. Chem. B, 106 (49), 12644–12667
(2002).
30K. Malek and M. O. Coppens, "Knudsen self- and Fickian diffusion in rough nanoporous
media," J. Chem. Phys., 119 (5), 2801–2811 (2003).
31D. G. Levitt, "Dynamics of a single-file pore - non-Fickian behavior," Pys. Rev. A, 8 (6), 3050–
3054 (1973).
32P. Castiglione, A. Mazzino, P. Muratore-Ginanneschi, and A. Vulpiani, "On strong anomalous
diffusion," Phys. D (Amsterdam, Neth.), 134 (1), 75 – 93 (1999).
33D. R. Gaskell, An introduction to transport phenomena in materials engineering, Macmillan
Pub. Co., 1992.
34S. Lagergren, "Zur theorie der sogenannten adsorption geloster stoffe," K. Sven.
Vetenskapsakad. Handl., 24 (4), 1–39 (1898).
6. Acknowledgements
We would like to thank Lakshmi Krishna and Ed Laitila for their assistance with the x-
ray diffraction analysis, Lei Zhang for her help in performing the TGA experimentation, and
20
David Hand for an intellectually stimulating discussion on the topic of adsorption/diffusion.
Thanks, also, to Kim Bowen and Emily Shearier for their time spent editing and proofreading.
We would also like to acknowledge the 2009 archaeological field team; Steen and Mark
Matheson of Parowan, Utah; Todd Prince, Park Manager, Frontier Homestead State Park
Museum and Karen Krieger, Deputy Director Administration, Utah State Parks, Department of
Natural Resources for their assistance in obtaining the samples and information necessary to
perform this study.
21
Fig. 1. X-Ray diffraction results for the Davenport pottery sample. Peaks are labeled by the
corresponding phase: Al-albite, An-anorthite, B-biotite, C-calcite, D-diopside, H-
metahalloysite, He-hematite, I-illite, M-mullite, Q-quartz, R-rutile, and Sa-sanidine.
Fig. 2. Thermogravimetric analysis and differential TGA curves for a 19th century
archaeological (Davenport) ceramic sample.
Fig. 3. Observed dehydration mass curve for samples 2 (square), 3 (circle), and 4 (diamond) for
drying performed prior to experiment 2. The inset (same axes and units) is a log-log
presentation of the data, which uses absolute fractional mass. These mass-loss data
exhibit both dehydration and slow dehydroxylation behavior, as evidenced by their non-
asymptotic behavior.
Fig. 4. The observed rehydration/rehydroxylation mass gain curve for sample 4 in experiment 3
(triangle, solid line), which was held at room temperature and sample 2 in experiment 4
(circle, dotted line), which was held at a low temperature.
Fig. 5. Illustration of the additive behavior of the empirical equation developed to describe
rehydration/rehydroxylation behavior of sample 2 in experiment 4. The solid line
represents the total mass predicted, the dashed line is the first term describing rehydration
behavior, and the dashed-dotted line is the second term, describing rehydroxylation. The
inset image (same axes and units) illustrates the behavior of the empirical equation and its
components over short time period.
Fig. 6. Temperature dependence of the rehydration/rehydroxylation exponent, n, in
rehydroxylation experimentation. Circles indicate rehydroxylation processes, and
triangles represent dehydration. Note that n~4 at room temperature (298 K, or 25°C).
22
Horizontal error bars represent one standard deviation in temperature and vertical error
bars represent the 95% confidence level of the rehydroxylation exponent.
Fig. 7. Visualization of the correlation between fluctuations in humidity and in observed mass
for sample 2 from experiment 2. The solid vertical and dashed lines represent peaks and
depressions in mass and humidity, respectively. The inset figure illustrates the effect of
humidity fluctuations on the deviation of the instantaneous from the mass predicted by
using Equation 2.
23
Table 1: Samples used for experimentation and characterization
Sample Purpose Mass (g)
Sample 1 Rehydration/Rehydrox. 96.0
Sample 2 Rehydration/Rehydrox. 58.7
Sample 3 Rehydration/Rehydrox. 34.5
Sample 4 Rehydration/Rehydrox. 32.5
XRD Fragment Powder Diffraction ~5
TGA Fragment TGA Experimentation 0.024
Table 2: Experimental and environmental parameters for each sample
Experiment Sample T Range DHX T (°C)
Mean T ± s (°C)
Mean RH ± s (% Rel. Humidity)
1 1 Room 500 ~23† -
2 - DHX 2 Dryer - 105 ± 7.00‡ -
2 - DHX 3 Dryer - 105 ± 7.00‡ -
2 - DHX 4 Dryer - 105 ± 7.00‡ -
2 - RHX 2 Room 650 22.7 ± 0.18 21.0 ± 1.4
2 - RHX 4 Room 650 22.6 ± 0.24 20.0 ± 1.1
3 2 High 650 80 ± 7.00‡ -
3 3 Low 650 -1.3 ± 0.73 27.7 ± 2.6
3 4 Room 650 22.9 ± 0.15 24.7 ± 2.8
4 2 Low 650 3.4 ± 0.32 27.6 ± 0.3 † Estimated temperature ‡ Estimated associated error
24
Table 3: Normalized (fractional) rehydration/rehydroxylation fit parameters for all valid
mass gain data. Errors for n are at 95% confidence.
Experiment Sample T Range α (hr-1) β (g/g) γ (hr-1/n) n
1 1 Room 0.3496 0.0007 0.0003 3.5 ± 0.8
2 - DHX 2 Dryer 0.0101 0.0004 -0.0032 9.7 ± 0.8
2 - DHX 3 Dryer 0.0087 -0.0001 -0.0030 9.5 ± 0.3
2 - DHX 4 Dryer ~0.0000 ~0.0000 -0.0032 10.3 ± 0.4
2 - RHX 2 Room 0.2786 0.0011 0.0002 3.0 ± 1.0
2 - RHX 4 Room 0.7108 0.0010 0.0003 3.8 ± 1.6
3 2 High -† -† 0.0004 5.7 ± 0.4
3 3 Low 0.3347 0.0010 0.0002 2.9 ± 0.4
3 4 Room 0.0039 0.0041 0.0008 3.8 ± 1.1
4 2 Low 0.4601 0.0013 0.0003 2.3 ± 0.3 † Sample 2 from experiment 3 required a fit with 2 alpha and beta parameters
25
Figure 1
Figure 2
5
15
25
35
45
10 12 14 16 18 20 22 24 26 28 30 32 34
Inte
nsity
(CPS
)
Double Angle, 2θ (o)
Q Q
An/AlM I
An H
SaA
n Al
Sa/A
nSa
/An H/A
l
IM
Sa
R
C/D
R/A
n/A
l
Sa
An
D
SaQ/He
B
-0.0006
-0.0004
-0.0002
0.0000
-0.04
-0.03
-0.02
-0.01
0
0.01
350 450 550 650 750 850 950
Diff
eren
tial M
ass (
K-1
)
Nor
mal
ized
Mas
s, ∆m
/m0
(g/g
)
Temperature (K)
DTGA
TGA
26
Figure 3
Figure 4
-0.006
-0.005
-0.004
-0.003
-0.002
0 50 100 150 200 250 300
Frac
tiona
l Mas
s, ∆m
/m0
(g/g
)
Dehydration/Dehydroxylation Time (hr)
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0 50 100 150 200 250 300 350 400 450 500
Nor
mal
ized
Mas
s, ∆m
/m0
(g/g
)
Time from Dehydration/Dehydroxylation (hr)
Sample 4, Experiment 3Room Temperature (22.8°C)
Sample 2, Experiment 4Low Temperature (3.4°C)
0.102 ± 0.005
0.001
0.010
1 100
|∆m
/m0|
27
Figure 5
0.000
0.002
0.004
0.006
0.008
0 300 600 900 1200 1500 1800
Nor
mal
ized
Mas
s, ∆m
/m0
(g/g
)
Time from Dehydration/Dehydroxylation (hr)
0.000
0.001
0.002
0.003
0 10 20 30
28
Figure 6
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
265 280 295 310 325 340 355 370 385
Reh
ydro
xyla
tion
Exp
onen
t, n
Temperature (K)
Rehydration/Rehydroxylation
Dehydration
29