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X-ray fluorescen
Cite this: Anal. Methods, 2017, 9, 2371
Received 21st March 2017
DOI: 10.1039/c7ay90044a
rsc.li/methods
This journal is © The Royal Society of C
ce (XRF) analysis of porcelain:Background paper
Analytical Methods Committee AMCTB No. 77
This technical brief outlines how X-ray fluorescence (XRF) can
be used
for the investigation of cultural heritage objects made of
porcelain. It
discusses the types of questions that can be answered with XRF
and
provides an overview of how the method works.
X-ray uorescence (XRF) is a non-destructive analytical
methodthat allows the identication and quantication of the
chemicalelements present in the surface of a wide variety of
objects. It iscurrently widely applied in the investigation and
character-isation of art objects as well as geological and
archaeologicalmaterials. Because XRF is non-destructive, the method
isparticularly suitable for the analysis of complete objects,
suchas porcelain vessels, when sampling is not an option because
itwould affect the integrity of the item. In the last 20
years,portable instruments have become commercially
available,allowing samples or objects to be analysed in situ (see
AMCTechnical Brief No. 41). Most XRF instruments are capable
ofdetecting the majority of elements in the periodic table,
rangingfrom magnesium to uranium. This makes XRF an ideal tool
tocharacterise the materials used in the manufacture of
porcelainbodies, glazes, enamel decoration and gilding.
Types of porcelain
There are two main types of porcelain, dened by
chemicalcomposition and ring temperature: hard paste and so
paste.
Hard paste ‘true’ porcelain is a hard white ceramic that wasrst
produced in China and later in Japan and Europe. It is
hemistry 2017
made from kaolinite clay and petuntse (a rock comprising
mica,feldspar and quartz).
So paste porcelain is a less translucent, slightly porouswhite
ceramic that began to be manufactured in Europe in the18th century,
although there were attempts at production in thepreceding
centuries. It is made from white clay mixed witha glass frit (sand,
gypsum, soda, salt, alum and nitre) fusedtogether with chalk and
lime.
Bone china is a porcelaneous body that was developed inBritain
in the 18th century and is considered to be a type of sopaste. It
is composed of kaolin/ball clay and Cornish stonemixed with a bone
ash ux. Both so paste and bone chinawares were rst produced in
imitation of the ‘true’ hard pasteporcelain as the hard paste
formula and raw materials were notwidely known at the time.
Porcelain is typically coated with a silica-rich glaze, whichhas
a chemical composition that is compatible with the paste.For
example, hard paste glazes consist of silica with an alkalisuch as
lime or potash and so paste glazes are based on silicawith lead
oxide. A range of decorative components can beapplied, including
underglaze, in-glaze, on-glaze (enamel) andgilded decoration.
Porcelain colours are made from pigments,such as oxides of copper,
cobalt and iron, which producea range of shades depending on the
ring conditions and typeof glaze to which they are applied.
Applications of XRF analysis
XRF is used on porcelain and its decorative components inorder
to help answer questions on authenticity, provenance,date and
restoration. The raw materials and recipes employedby different
production centres result in unique chemicalcompositions that can
be determined by using XRF. Rawmaterials oen changed over time,
possibly owing to techno-logical or economic considerations. Each
time a new recipe wasused, the composition would be subtly
different. An example ofone of these changes involved the use of
green enamels at theMeissen factory in Saxony. In the 18th century,
green enamels
Anal. Methods, 2017, 9, 2371–2374 | 2371
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Analytical Methods AMC Technical Briefs
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were coloured using copper oxide but, at the beginning of
the19th century, chromium oxide green was introduced. Thus
thepresence of chromium green is a good marker for 19th
centurydecoration. Temporal compositional differences form the
basisof scientic dating for most types of porcelain. In order for
thisdating to be effective, results must be compared with
databasescompiled from the analysis of established materials, or
newreference objects must be analysed.
Fig. 2 Handheld XRF.
X-ray fluorescence
XRF is a method that can determine concentrations of major,minor
and, in some cases, trace elements by using X-rays.The most common
XRF set-up used in heritage laborato-ries is energy dispersive (ED)
XRF. During an ED-XRFexperiment, a high-energy X-ray beam hits the
surface ofthe object or sample under observation. This in turn
emits X-rays of lower energy, a behaviour known as
‘uorescence’.Each chemical element produces uorescent X-rays
withenergies that are unique to that element. The emitted X-raysare
displayed as a spectrum with peaks of varying heights atdifferent
energies. The energy of a peak identies thechemical element
producing it and the height of a peak canusually be linked to the
abundance of that element in thesample. Soware is then used to
measure and quantify theabundance of detected elements. Reference
materials arealways used to calibrate the procedure or to check for
bias inthe results.
Equipment and methods
The three most common instruments used in heritage labora-tories
are (Fig. 1 and 2):
� Benchtop analysers,� Mobile open architecture instruments for
use in museum
galleries, and� Handheld analysers.
Fig. 1 Benchtop XRF.
2372 | Anal. Methods, 2017, 9, 2371–2374
Benchtop XRF instruments have a large chamber in whichthe object
for analysis is placed. These instruments have anadjustable beam
diameter, usually between 0.2 and 3 mm,which means that ne areas of
paint and gilding can be ana-lysed. Some benchtop instruments can
map elemental distri-butions spatially across the surface of the
object, allowingvariations in the pigments to be viewed visually
(Fig. 3).
Mobile models have comparable beam sizes (0.2 to 1.5 mm),but
have the added benet of being able to work on largeimmoveable
objects in situ. Benchtop and mobile devices areoperated in
combination with soware on a connectedcomputer.
Handheld devices are fully portable, weighing only a
fewkilograms, which means that they can be easily carried
intomuseums, private collections and auction houses, and
thatvaluable objects no longer need to be transported to the
labo-ratory. The beam size is larger and usually non-adjustable
onhandheld devices, with beam sizes ranging from 3mm to
8mm.Handheld devices are operated via soware on the back of
theinstrument or by connecting them to laptop computers. Ashandheld
and mobile instruments have open X-ray beams, theinstruments must
be used within a controlled area and theoperator has to abide by
strict health and safety regulations.
In order to conduct an analysis, the whole object is
placedeither in the chamber (for benchtop instruments), or directly
infront of the instrument head within 1 cm of the beam on themobile
or handheld device. Sampling is not required and themethod is
completely non-destructive. Handheld devicesusually have to touch
the object to reduce radiation scatter.Measurement times typically
range from 30 to 100 seconds.Longer measuring times are required
for the detection of ‘light’elements (those of low atomic number
such as sulfur,aluminium and silicon) and trace elements (those at
concen-trations lower than roughly 0.1% by mass). Shorter
measuringtimes are oen employed for handheld devices as it can
bedifficult for the operator to hold the XRF in position for
longperiods.
This journal is © The Royal Society of Chemistry 2017
http://dx.doi.org/10.1039/c7ay90044a
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Fig. 3 Visual appearance (top) and XRF map (bottom) of iron
distri-bution across the surface of an enamelled porcelain
plate.
Fig. 4 Example of an XRF spectrum of gilding on porcelain.
Fig. 5 XRF spectra of chromium green (green spectra) and
coppergreen (red spectra) enamels.
AMC Technical Briefs Analytical Methods
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Results and interpretation
Three types of output can be generated by XRF instruments:
anX-ray spectrum, a list of spectrum peak areas, and
relativeconcentrations calculated via calibration data. The raw
outputis displayed as a spectrum, with each peak uniquely
repre-senting a particular chemical element (Fig. 4). Each peak
isidentied with the originating element by using sowareinstalled on
the instrument or on a connected computer. Theheight of each peak
is related to the abundance of the element.Several spectra can be
overlaid on the screen allowing the userto discern visually the
differences between the ranges andabundances of elements in
different targets.
This journal is © The Royal Society of Chemistry 2017
Because of this, spectra provide a useful means to charac-terise
a material quickly. For example, the colouring agent ina green
enamel may be identied as copper or chromium(Fig. 5), or a glaze
may be characterised as leaded or non-leadedby the presence or
absence of high lead peaks. The character-isation of the basic
materials can be useful for cataloguingpurposes, documenting the
history of technology, assessmentof the condition of an object,
identifying restorations andrepairs, and dating.
Quantitative analysis
Some types of XRF soware can calculate and compare the sizeof
the elemental peaks on the spectrum: this is called ‘peak
areaanalysis’ and allows the user to determine the relative
propor-tions of elements present. The data can be downloaded
andused in statistical soware packages. Peak area analysis is
usedto nd simple patterns in the data that may indicate the use
ofdifferent recipes or sources of rawmaterials. For example, at
theMeissen factory, early 18th century porcelain pastes and
glazeswere produced by using a calcium sulfate ux that was
lateraugmented and replaced by a potassium feldspar ux. Theseux
materials may be identied using peak area analysis byexamining the
ratio of calcium to potassium (Fig. 6). As these
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Fig. 6 Scatter plot of Meissen glazes produced in 1715–74,
high-lighting the high calcium/low potassium composition of early
glazes.
Analytical Methods AMC Technical Briefs
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different uxes were used at different dates, this type of
infor-mation can be used as an aid to dating.
A more general type of analytical result comprises deter-mining
concentrations of the elements (as contrasted withelemental
ratios). These are calculated from peak areas but inconjunction
with information from reference materials con-taining known
concentrations of the elements. Some XRFinstruments have in-built
theoretical ‘fundamental parameter’(FP) programs to calculate
percentage data, based on both themeasured peak intensities and the
fundamental physicsspecic to that instrument and the elements
concerned. Resultsare normalised to 100% and are material-specic.
FP programsare calibrated by using a specic set of elements, so if
an objectunder test has a different suite of elements the
normalisedquantitative results will be inaccurate. The accuracy of
theseprograms must therefore be checked with a reference
materialsimilar to the test object.
The widely-recommended way to generate accuratepercentage data
is to conduct an ‘empirical calibration’wherebythe operator
calibrates the instrument using a set of referencematerials with
known compositions similar to the test material.A second (disjoint)
set of reference materials is then analysed tocheck the accuracy of
the calibration. The calibration can thenbe used to determine the
composition of the porcelain underanalysis.
Care must be taken in attempting to analyse thin layers oflight
material as the X-ray beam can penetrate into the substratematerial
and the results may represent a mixture of one or morelayers.
Analysis depth is typically in the region of 40 mm(micrometres) for
a high lead glaze or 500 mm for a lime-alkaliglaze. Heterogeneity
of the material will reduce the reliabilityof the results, and
therefore several readings should be takenfrom nearby areas and the
results averaged.
In order that useful interpretations may be made, resultsmust be
compared against a database of established materialsor by
conducting XRF analyses of comparable reference objects.
2374 | Anal. Methods, 2017, 9, 2371–2374
Published databases can be found in academic journals such
asArchaeometry, Journal of Archaeological Science, X-Ray
Spectrom-etry and Journal of the American Ceramic Society.
Useful literature
A. Bezur and F. Casadio, The analysis of porcelain usinghandheld
and portable X-ray uorescence spectrometers, inHandheld XRF for Art
and Archaeology, Studies in ArchaeologicalSciences 3, ed. A. N.
Shugar and J. L. Mass, Leuven, LeuvenUniversity Press, 2012.
F. Casadio, A. Bezur, K. Domoney, K. Eremin, L. Lee, J. L.Mass,
A. Shortland and N. Zumbulyadis, X-ray uorescenceapplied to
overglaze enamel decoration on eighteenth- andnineteenth-century
porcelain from central Europe, Stud. Con-serv., 2012, 57,
61–72.
K. Domoney, A. Shortland and S. Kuhn, Characterization
of18th-Century Meissen Porcelain using SEM-EDS, Archaeometry,2012,
54(3), 454–474.
W. Kingery, The Development of European Porcelain,
HighTechnology Ceramics: Past, Present and Future. Ceramics
andCivilization III., The American Ceramic Society,
Westerville,1986, pp. 153–179.
X-Ray Fluorescence Spectrometry (XRF) in
Geoarchaeology,Springer, New York, ed. M. Shackley, 2011.
P. J. Potts and M. West, Portable X-ray uorescence analysis,AMC
Technical Briefs No. 41, 2009.
Portable X-ray Fluorescence Spectrometry: Capabilities for
InSitu Analysis, ed. P. Potts and M. West, Royal Society of
Chem-istry, Cambridge, 2008.
K. Yu, Attribution of antique Chinese blue-and-white porce-lains
using Energy Dispersive X-Ray Fluorescence (EDXRF), inRadiation in
Art and Archeometry, ed. D. Creagh and D. Bradley,Elsevier Science,
Amsterdam, 2000, pp. 317–345.
Kelly Domoney (Craneld University and Ashmolean
Museum,University of Oxford)
This Technical Brief was prepared by the Heritage
ScienceSubcommittee and approved by the Analytical MethodsCommittee
on 29/12/16.
This journal is © The Royal Society of Chemistry 2017
http://dx.doi.org/10.1039/c7ay90044a
X-ray fluorescence (XRF) analysis of porcelain: Background
paperX-ray fluorescence (XRF) analysis of porcelain: Background
paperX-ray fluorescence (XRF) analysis of porcelain: Background
paperX-ray fluorescence (XRF) analysis of porcelain: Background
paperX-ray fluorescence (XRF) analysis of porcelain: Background
paperX-ray fluorescence (XRF) analysis of porcelain: Background
paperX-ray fluorescence (XRF) analysis of porcelain: Background
paper
X-ray fluorescence (XRF) analysis of porcelain: Background
paper
