A introduction to Rehydroxylation dating

A introduction to
Rehydroxylation dating

Contents
 Introduction .................................................................................................... 3
   The RHX Revolution ........................................................................................ 4
   What happens when clay is fired in a kiln? ..................................................... 5
   Does fired clay change over time? .................................................................. 8
   How can rehydroxylation date fired clay? ....................................................... 9
   Dating archaeological ceramics ..................................................................... 12
   Development of RHX..................................................................................... 13
   What is RHX? The science and theory behind rehydroxylation ..................... 15
   How does RHX work? The method for rehydroxylation dating fired clay ....... 18
   Measuring RHX ............................................................................................. 19
   Challenges of RHX ......................................................................................... 20
   A timeline of RHX development .................................................................... 24
   Frequently Asked Questions ......................................................................... 26

The RHX dating method uses a moisture-based internal clock for dating archaeological ceramics.
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                                                                                                                       2

Introduction
    The long-term moisture expansion of bricks has been known to
    structural engineers for some time, as it is the cause of cracking in
    brick masonry due to expansive stresses. Research at The Universi-
    ties of Manchester and Edinburgh has shown for the first time that
    this process happens at a constant, but diminishing, rate over
    thousands of years. This research was the precursor to a new
    method of dating archaeological ceramics.

    Rehydroxylation can provide a date of manufacture for archaeo-
    logical ceramics by measuring the lifetime mass gain. The method
    is self calibrating, so avoids any problems due to differences in fir-
    ing temperature, mineralogy and microstructure.

    Ceramics, pottery or “pot” is arguably the most ubiquitous find on
    archaeological sites worldwide. The predictable uptake of environ-
    mental moisture in fired clay material via rehydroxylation (RHX)
    provides, for the first time, a method of directly dating archaeo-
    logical ceramics.
    Rehydroxylation (RHX) dating is perhaps the technique archaeology
    has been waiting for.

3

The RHX revolution
Rehydroxylation is the super slow, progressive chemical recombina-
tion of environmental moisture with fired-clay material. Research in
rehydroxylation rapidly evolved from the prediction of expansion in
structural masonry to an independent method of dating archaeo-
logical ceramics.

All fired clay - bricks, tiles, pottery – expand on aging due to the up-
date of moisture. In fact, long term moisture expansion is a well-
known property of fired clay materials, such as bricks, but its’ appli-
cation to date archaeological and historic fired-clay is one of the
most exciting developments in archaeological science since the in-
troduction of radiocarbon dating in the 1950’s for organic material.
RHX dating can provide a date of manufacture for archaeological ce-
ramics by measuring the lifetime mass gain of the ceramic. This is
the story of how the ability to predict expansion in structural ma-
sonry came to be used to date archaeological ceramics.

                                                                           4

What happens when clay is fired in a
    kiln?
    Once a potter has made a shape out of clay, they fire it in a kiln it to
    remove all the moisture from the clay so that it will stay the same
    shape. At high temperatures, above 500°C, so much moisture is re-
    moved from the clay that it is transformed into ceramic.
    As anyone who has ever been to a pottery class will know, water is
    added to raw clay so it becomes malleable, enabling it to be formed
    into and hold a desired shape. The formed clay then has to be left to
    air dry until it becomes “leather hard”. At this stage most of the water
    added to help shape the clay has evaporated away. This is an impor-
    tant step, otherwise when it is fired any trapped water will convert to
    steam, creating enough pressure to rupture the vessel, spoiling all
    your hard work. However, when “leather hard” there is still some wa-
    ter within the clay, this water is chemically bound up within the min-
    erals that make up the clay. During firing in a kiln, this “chemisorbed”
    or structural water is removed from within the matrix of the clay. The
    removal of chemisorbed water is part of the chemical transformation
    that occurs at high temperatures in the kiln that turns clay into ce-
    ramic.

    Absorption means filling of pores in a solid, so clay absorbs the water
    added to help shape it. A bath sponge or your clothes, for example,
    also absorb water; this absorbed water can be easily removed by dry-
    ing at room temperature.
    Adsorption is the binding of molecules or particles to a surface, so
    this is the chemisorbed water that is bound up in the clay matrix. This
    chemisorbed can only be removed from the clay by heating to very
    high temperatures, this process is called dehydroxylation. However,
    the fired clay starts to replace the chemisorbed water as soon as it is
    removed from the kiln, this is rehydroxylation.
5

Does fired clay change over time?
Yes, the process of readsorbing water in bricks, which we now call re-
hydroxylation (RHX), has been known about for a long time. There
was a tradition amongst bricklayers to never use bricks straight from
the kiln but to leave them for a fortnight to “mature”. Did you know a
single brick, like those used to build houses, can absorb a pint of wa-
ter!

We know now that this tradition was because the bricks were going
through the most rapid phase of readsorption, which led the bricks
expanding. This expansion is actually continuous, but super slow, and
did not become a problem until the introduction of hard cement-
based mortars. Previously, lime-based mortars had been used which
were able to absorb the expansive strains as the bricks expanded dur-
ing the lifetime of the structure. The use of cement-based mortars in
modern masonry required the introduction of expansion joints to ac-
commodate this long term moisture expansion, as well as thermal ex-
pansion, of bricks and so prevent damage to the overall structure.
Therefore it became necessary to be able to estimate the magnitude
of this expansion over the lifetime of new structures.

Those with an interest in antiques may have observed crazing in the
glaze of some old ceramics. This was first reported by H. Schurecht in
the 1920’s, who suggested that it was due to the ceramic expanding
more than the glaze, causing the glaze to crack. He hypothesised that
the ceramic was readsorbing from moisture in the atmosphere, re-
placing the chemically bound water that had been driven off during
firing. To support this hypothesis he was demonstrated that white-
ware ceramics, with evidence of crazed glaze, would contract when
reheating to 500°C.

                                                                          8

How does RHX work?
    The slow progressive chemical recombination of ceramics with envi-
    ronmental moisture, rehydroxylation (RHX) provides the basis of this
    archaeological dating technique. Water as vapour readily permeates
    the entire macropore system of ceramic material. The rate-
    determining rehydroxylation reaction proceeds by ultraslow nano-
    scale solid-state transport (single file diffusion) from the macropore
    surfaces into clay matrix. The measurement of mass gain kinetics, to-
    gether with total mass gain since manufacture (obtained by reheat-
    ing), provides an accurate self-calibrating method of archaeological
    ceramic dating.

    Rehydroxylation rates are described by a (time)1/4 power law. Two dis-
    tinct stages are seen when ceramics, both in the freshly fired state
    and after reheating, react with environmental moisture. The brief first
    stage, which lasts only for a few hours, is much more rapid than the
    second stage, which continues indefinitely. A ceramic sample may be
    dated by first heating it to determine its lifetime water mass gain, and
    then exposing it to water vapour to measure its mass gain rate and
    hence its individual rehydroxylation kinetic constant. The kinetic con-
    stant depends on the temperature the measurements are taken at.

    We exploit these properties of fired ceramic in RHX dating, to provide
    a method of determining the age of ceramic artefacts. This method
    will provide an estimate of either the date an object was fired or the
    date it was last heated to over 500°C.

9

A piece of 18th
                                                                           century Coal-
                                                                           port bone china,
                                                                           as seen through
                                                                           a microscope,
                                                                           this shows how
                                                                           porous ceramic
                                                                           is, particularly
                                                                           when compared
                                                                           to the glaze ©
                                                                           Dr. Robert Freer

A schematic showing the basic principle behind the RHX dating technique.
                                                                                        10

What is RHX?
Rehydroxylation (RHX) is the chemisorption of water by fired clay ce-
ramic and it occurs by the diffusion of water molecules along random
linear pathways through the solid ceramic. This long-term uptake of
water is both very small and gets progressively slower, so that the wa-
ter demand is extremely modest. As the rehydroxylation rate is con-
trolled entirely by internal processes, it does not increase when water
is available in excess in the microenvironment.

During firing, clay first loses weakly bound molecular water and then
at temperatures in the range 450–900◦ C water is lost from the octa-
hedral sheets by chemical dehydroxylation 2OH-→H2O + O2-. However,
in many clay ceramics these reactions are evidently incomplete. After
cooling, slow rehydroxylation of partially reacted ceramic material oc-
curs. Consequently, the reactivity of the ceramic with moisture is di-
rectly related to the crystallinity of the fired clay.

The chemisorption process in ceramic material is a diffusion con-
trolled rehydration reaction. The single file nature of this diffusion im-
plies that the water molecules are so constrained by the diameter of
the pathways that they cannot pass each other. As the queue of mole-
cules diffuses along such a pathway, the leading molecule will react
with the first available reaction site and will thereby be removed from
the diffusion process by an annihilation reaction of the form A + B→
0.

Our data on expansion and mass gain kinetics in ceramics are thus far
unique in providing experimental evidence for the process of single
file diffusion.

                                                                             12

The RHX dating methodology

     In principle the RHX dating methodology is simple, however produc-
     ing data of sufficient quality to provide an estimate of age for a
     piece of fired ceramic is more challenging.

     First the sample is dried at 105°C until it reaches constant mass, m1.
     At this point all physically absorbed moisture is driven off and only
     the chemisorbed water acquired over the sample’s lifetime remains.

     The sample is then placed under specific and carefully controlled
     conditions of temperature and relative humidity and is left until the
     sample comes into equilibration with these conditions.

     Once the sample has equilibrated, the initial sample mass m2 , is
     measured. This initial mass represents the mass of the ceramic plus
     the amount of water adsorbed via RHX by the ceramic over its life-
     time under these conditions of temperature and relative humidity.

     The sample is then heated to 500°C until it is “emptied” of all water
     both physisorbed and chemisorbed, m3. As for m1 the mass loss is
     monitored until it reaches constant mass.

     The sample is then placed under the same carefully controlled con-
     ditions of temperature and relative humidity that were used to ob-
     tain m2 and again the sample is left to come into equilibration with
     these conditions.

     The data from this early time mass gain following reheating to 500°C
     show a characteristic 2-stage mass gain process.

     Stage I is the sample cooling from 500°C and coming into equilibra-
     tion with the ambient conditions.

     Stage II is the mass gain due only to the rehydroxylation process, it is
     only this part of the mass gain, from m4, which is extrapolated to m2
     and gives the age determination.

13

An illustration of how
                            one sample required
                            167 hours of drying
                            time until it reached
                            constant mass. The
                            mass loss was moni-
                            tored after 17, 48, 117
                            and 167 hours at 105°C

This graph shows raw
experimental data to
demonstrate the level of
precision that it is nec-
essary for RHX dating.
This can only be
achieved by maintaining
constant conditions of
temperature and rela-
tive humidity.

                             This graph also shows
                             raw experimental
                             data. Only the section
                             of the data highlighted
                             red is used to calculate
                             the RHX rate constant.
                             Before that the ob-
                             served mass gain is
                             due to several proc-
                             esses occurring simul-
                             taneously.               14

The science and theory behind RHX
     The mass gain due to RHX will increase incrementally as each water
     molecule combines in turn. We measure mass gain, as it is the more
     fundamental measure of the underlying process; expansion is a conse-
     quence of this. The rates of mass gain are extremely slow but the use of
     an accurate recording microbalance with controlled sample environ-
     ment makes the determination of rates of reaction with water vapour
     by measurement of mass entirely feasible.

     We have identified three different types of water that are present
     within the matrix of fired-clay ceramic after heating to 500°C. It is im-
     portant to differentiate between them, as when attempting to date
     fired ceramic material via RHX it is only the chemisorpbed water that is
     of interest.

     TYPE 0, physically absorbed water that is held within the matrix and is
     present as liquid water. The loss and gain of this TYPE 0 water is more
     accurately described as dehydration and rehydration respectively.
     TYPE 1, physically adsorbed water that is loosely bound to the internal
     surfaces of the ceramic matrix. If TYPE 1 is lost below 200°C it is still
     classed as dehydration.
     TYPE 2, chemically adsorbed water. This is also referred to as
     “structural” water as it is the hydroxyl groups bound within the alumi-
     nosilicate mineral that makes up the amorphous component of the ce-
     ramic matrix. The loss and gain of this water is dehydroxylation and re-
     hydroxylation respectively and it only occurs at temperatures above
     500°C.
     Therefore to date fired ceramic material by RHX we need to be able to
     isolate and measure the rate that structural hydroxyl groups are recom-
     bining with the aluminosilicate mineral, the Type 2 water.
15

Mass gain versus time1/4 following reheating at 500°C
(a) The characteristic two stage mass gain. This is the combined mass gain of all the three
    types of water identified T0+T1+T2 (T012) (~27,000 data points). The contribution these
    components make can be separated out as shown by graphs (b) and (c)
(b) This is mass gain due to T0+T1 (T01) only and this eventually stops when the sample
   has equilibrated with the ambient conditions. This mass will track any changes in tem-
   perature or relative humidity.
(c) This mass gain due to the T2 rehydroxylation component only. © Archaeometry.              16

Dating archaeological ceramics
Archaeologists use ceramics to reconstruct past human behaviour and
finding something that was made and used by another person hun-
dreds or thousands of years ago, is a unique experience. The dating of
archaeological ceramics by typology or style usually provides one of
the first indications of how old an archaeological site is.

The archaeological applications of the long term mass gain due to re-
hydroxylation of ceramics is as a dating tool. Depending on the period
of history, dating a site by the shape and decoration of the recovered
ceramics can be vague and unsatisfying or even hotly debated, but
there has not been an alternative method available. RHX dating could
provide a method of dating when a piece of fired clay was removed
from the kiln, whether this was hundreds or even thousands of years
ago.

                                                                         18

Measuring RHX
     Rehydroxylation is a super-slow chemical reaction, where atmospheric
     moisture is chemically recombined into fired ceramic material via a
     nano-scale process called single file diffusion. This leads to expansion
     and mass increase of the ceramic material. As we reduced the sample
     size from 2.5kg we needed to use more sensitive equipment to iden-
     tify these very small changes in mass. For this we use a gravimetric
     water vapour sorption analyser. The technique involves very accu-
     rately measuring the weight change of samples after they have equili-
     brated at a specific temperature and relative humidity. The weights of
     the samples are constantly monitored and recorded as the tempera-
     ture and relative humidity are held constant.

     As rehydroxylation is a chemical process, the rate of reaction is tem-
     perature dependant. Therefore it is necessary to provide an estimate
     of the temperature that an individual object has been exposed to dur-
     ing its lifetime (i.e. since manufacture). We have developed a model
     based on climatic data that can calculate the Effective Lifetime Tem-
     perature (ELT) for most locations worldwide over the last 5000 years
     to with 0.1°C . As the ELT takes account of the activation energy of the
     RHX reaction, it is more sophisticated than a mean temperature.

     Relative humidity describes the amount of water vapour in a mixture
     of air and is used when the rate of water evaporation is important.
     Did you know that the air in Cairo contains much more water vapour
     than the air in Manchester! This is because the higher the air tem-
     perature, the more water vapour it can hold.
     Cairo (hot and dry): Average temperature = 32.2 OC (90 OF) and rela-
     tive humidity = 46% (of 15g/m2 of water vapour)
     Manchester (cold and wet): Average temperature = 12.8 OC (55 OF)
     and relative humidity = 67% (of 6.6g/m2 of water vapour).
19

Challenges of RHX—technical
Measuring the very small changes in mass associated with rehydroxy-
lation is difficult. This is partly due to the very small increases in
weight involved and partly because it is a chemical reaction.

As rehydroxylation is based on a chemical reaction, it means that the
rate of mass increase will change with temperature. Therefore we
need to carefully monitor the temperature, and then we can use the
Effective Lifetime Temperature and the Arrhenius equation to calcu-
late the rate that would have occurred over the lifetime of the arte-
fact. We have been working closely with the instrument manufactures
to try and improve our ability to measure all of these aspects. For
those who want to adapt a microbalance for RHX work, we have pro-
duced a guide to setting up the microbalance to meet the RHX data
collection requirements.

As the mass changes associated with RHX are very small, typically a
20mg increase for a 4g sample over a three day experiment, we have
also discovered that it is necessary to take measurements under
tightly controlled conditions of relative humidity. Any mass gain asso-
ciated with the material equilibrating to fluctuating amounts of mois-
ture in the air can mask the mass gain due to rehydroxylation.

Furthermore, we have discovered that some types of ceramic material
are more amenable to the measurement of the RHX reaction than
others. Depending on the firing conditions, differing amounts of the
clay matrix would have become crystalline. With some types of ce-
ramic material, such as porcelain, the majority of the clay would have
been vitrified. This means that with porcelain there is insufficient re-
active material within the ceramic for us to be able to detect the mass
gain with currently available instrumentation.
                                                                           20

Challenges of RHX—material
     Following the success of RHX on tiles, we have encountered three
     main challenges in applying RHX dating to archaeological fired-clay
     material:
     1) The presence of non-refractory contaminants
     2) The effect of burial on the temperature history compared with that
          of material from standing structures
     3) Storage in a museum, which could potentially cause a significant
          change in average lifetime temperature of an artefact

     Often with archaeological artefacts, materials have been added to the
     clay in order to make ceramics. This was either for technological rea-
     sons, like organic and inorganic tempers, or through use such as resi-
     dues and these are “RHX contaminants”. This means that they inter-
     fere with our ability to identify the very small changes in mass that oc-
     cur during rehydroxylation. Porcelain is also a problem as most of the
     ceramic body has been transformed, meaning that current instrumen-
     tation cannot detect the minute mass changes involved.

     Archaeological material has been buried for hundreds or thousands of
     years and, depending on the burial environment, it could have under-
     gone other processes that may affect the rehydroxylation process. We
     have already identified a phenomenon which we have called the
     “museum effect”, the storage conditions in archives have a marked
     effect on RHX but this is something that once recognised we can ac-
     count for.

21

Redware clay oil
lamp from the Mero-
itic Period in Nubia
(300 BC-350 AD),
blacked by use ©
Manchester Mu-
seum.

                       Rim fragment from a
                       Predynastic vessel
                       (5500-3100 BC)
                       found in Hamma-
                       miya, Egypt. This
                       vessel was made
                       with straw temper
                       and has been black-
                       ened by fire © Man-
                       chester Museum

                                         22

From the original strain gauge used in the first experiments to measure the amount of strain
experience in fresh bricks, to the microbalance, a high-accuracy ultra-sensitive gravimetric bal-
ance, this can weigh samples under 5g to within ±0.1µg © CI Precision.

Development of RHX
Details of the journey that has been undertaken to discover the poten-
tial of rehydroxylation for dating archaeological ceramics.

1920’s Schurecht suggested that fired-clay expanded slowly as it reabsorbed mois-
ture from the atmosphere
1930’s Introduction of modern cement mortars led to the need to specify expan-
sion joints for brick masonry in design codes
1998 Measurement of the expansion of freshly fired bricks, and contractions of old
bricks
2003 Discovery of t1/4 law using data from a strain gauge
2003 Demonstrated that further expansion could be induced in a 2000 year old
brick by autoclaving
2003 First suggested the possibility exploiting this as a dating method
2008 Discovery of two stage expansion, initial dating methodology based on expan-
sion
2008 Discovered that expansion rate in reheated bricks reduces with each succes-
sive reheat
2008 Discovery of two stage mass gain, abandoned expansion-based method and
transferred to mass measurement
2008 Demonstrated that mass gain in reheated bricks is the same as freshly fired
bricks
2009 Dating experiments using modern bricks on a top pan balance
2009 Dating trials on bricks and tiles on a top pan balance of known age from Ian
Betts at MOLA
2009 CI Electronics began microbalance trials
2010 Discovered Arrhenius rate law dependence for Stage II, which requires that
measurements are done at the same temperature as the material had spent its life,
the Effective Lifetime Temperature (ELT)
2010 Reduced sample size from 2kg to

Frequently Asked Questions
     The 2009 paper in Proceedings of the Royal Society A generated a lot of
     interest and below is a collection of the top ten questions we received,
     along with our responses.

        Why do you heat to 500°C to remove the RHX water?
        In order to measure the amount of water that has been taken up by
            the ceramic via rehydroxylation we need to be able to remove the
            type 2 water without causing any change to the amorphous com-
            ponent of the ceramic, i.e. we want to return it to its’ as-fired state.
            There has been a lot of research done into the properties of ce-
            ramic materials by other research groups. Previous workers
            (Robinson 1985) have discovered that heating ceramics to 500°C
            returns it to its’ as-fired state.

        How can heating to 500°C for four hours remove thousands of years
            of accumulated RHX water?
        It doesn’t. Heating for four hours was suitable for the relatively mod-
            ern bricks that were measured in Wilson et al. 2009. We now rou-
            tinely heat at 500°C for 40 hours, weigh the sample, heat at 500°C
            for four more hours and weigh again. If the two weights are the
            same then we know the sample has fully dehydroxylated and pro-
            ceed with the analysis.

        What is the affect of different clay minerals or clay from different ge-
          ologies on RHX dating?
        We do not know, and this is part of what the current validation study
          will be examining. However, all clay minerals are aluminosilicates
          and essentially variations on a theme (Grim & Bradley 1948). Their
          crystal structures are arrangements of O- and OH- groups, typically
          20 oxygen ions to 4 hydroxyl groups, around various combinations
          of cations. We hypothesize that fine grained crystals will release
          their structural water more easily than larger grains but the RHX
          method is self calibrating for this affect.
25

Does the presence of a slip, glaze or surface decoration inhibit RHX
  dating?
Not at all, in fact the crazing of glazes was how this phenomenon
  was discovered. The first explanation given for the crazing ob-
  served in some glazed ceramics was that the ceramic expanding
  more than the glaze, causing the glaze to crack. It was suggested
  that the ceramic was readsorbing from moisture in the atmos-
  phere, replacing the chemically bound water that had been
  driven off during firing (Schurecht 1928). The current validation
  project will look at confirming this for archaeological material.

Does the use of grog (ground up ceramics) as a temper interfere
   with RHX dating? Would the age of a sample with grog temper
   come out too old?
No it should not. When the clay containing the grog temper is fired
   in a kiln the temperatures involved should dehydroxylate the grog
   as well as the fresh clay. The current validation project hopes to
   be able to confirm this by analysing archaeological material with
   grog temper.

Would the presence of organic residues present within a ceramic
  affect RHX dating?
We do not think that the presence of organic residues will interfere
  with the uptake of type 2 water but they would interfere with our
  ability to measure the amount of RHX water. The current valida-
  tion project will work with material that is known to be contami-
  nated with organic residues, visible (i.e. sooting) and absorbed
  (i.e. lipids) to determine what affect their presence has. It is
  mostly likely that these will have to be removed but there are es-
  tablish protocols for removing organic components from archaeo-
  logical ceramics.

                                                                        26

Does the depositional environment, i.e. waterlogged, marine,
        desert etc. affect the ability to date ceramics by RHX?
     No. The demand for type 2 or “RHX water” is extremely small.
        Therefore, in theory, it should not matter whether a sample is
        recovered from the bottom of the sea or the Atacama Desert.
        Again the current project aims to examine material from a
        range of archaeological contexts to determine if this is actu-
        ally the case.

     Does the type of soil matrix the ceramics were buried in affect
        the ability to date ceramics by RHX?
     Potentially, as the presence of soluble and insoluble salts within
        the ground water can interfere with our ability to measure
        the amount of type 2 water in a ceramic. Insoluble salts, car-
        bonates and sulphates, in particular have proven to be prob-
        lematic but these can be removed chemically. The current
        validation project will be testing to see if removal of insoluble
        salts from the ceramic matrix enables a sample to be dated
        by RHX.

     Why do you need to know the temperature the sample to be
        dated by RHX has been kept at?
     The rehydroxylation of ceramic material, the uptake of type II
        water, is a chemical reaction. All chemical reactions are tem-
        perature dependent, so the higher the temperature the faster
        the reaction occurs, and rehydroxylation is no exception. Wil-
        son et al. 2009 demonstrated that the rehydroxylation mass
        gain rate showed Arrhenius behaviour. Therefore once an ar-
        chaeological material has been recovered from the ground it
        will be exposed to higher temperatures, which accelerate the
        rate of the rehydroxylation mass gain. If this is not taken into
        account, relatively recent samples may be dated older than
        they actually are. As rehydroxylation is a super-slow chemical
        reaction the effect of this on ancient samples will be to in-
        crease the errors associated with the age estimate. Again,
        the validation project will be exploring these aspects.
27

Can you date by ceramic assemblage or authenticate my ceramic
      object?
   No. We currently can not currently offer any dating or authentica-
      tion services, because the RHX method is still undergoing devel-
      opment.

Grim, R. E. and W. F. Bradley (1948). "Rehydration and Dehydration of
the Clay Minerals." American Minerologist 33: 50-59.
Robinson, G. C. (1985). "Reversibility of Moisture Expansion." Ameri-
can Ceramic Society Bulletin 64: 712-717.
Schurecht, H. G. (1928). "Methods for testing crazing of glazes caused
by increases in size of ceramic bodies." Journal of the American Ce-
ramic Society 11(5): 271-277.
Wilson, M. A., M. A. Carter, et al. (2009). "Dating fired-clay ceramics
using long-term power law rehydroxylation kinetics." Proceedings of
the Royal Society A: Mathematical, Physical and Engineering Science
465(2108): 2407-2415.

                                                                          28

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                               March 2013