Low Frequency EPR of Ceramic and Marble Objects with Cultural Heritage Significance

Magnetic Resonance Laboratory, Rochester Institute of Technology, Rochester, NY 14623 L.E. Switala, M. Hoffman, W. Brown, W.J. Ryan, E.I. Hornak, N. Zumbulyadis, J.P. Hornak

Overview We report on a new application of low frequency EPR (LFEPR) to study ceramic and marble objects with cultural heritage significance. Conventional high field EPR has been used for this purpose by unobtrusively removing a small sample from the object. LFEPR is capable of looking at the EPR signal from large cultural heritage objects non-invasively and non-destructively.1,2 We have examined objects with the following width (w) and height (h) using a surface coil (SC).

1. W.J. Ryan, N. Zumbulyadis, J.P. Hornak, MRS Proceedings, mrsf13-1656-pp03-03 doi:10.1557/opl.2014.708 (2015).

2. J.P. Hornak, M. Spacher, R.G. Bryant, Meas. Sci. Technol. 2 (1991) 520-522. 3. S. Piligkos, et al., Molec Phys, 105 (2007) 2025–2030. 4. M. Bestmann, K. Kunze, A. Matthews, J. Struct. Geology 22 (2000) 1789-1807. 5. N.N. Lobanov, V.N. Nikiforov, et al., Doklady Chem. 426 (2009) 96-100. 6. R.S. de Biasin, et al., Ceramics International, 41(2015) 865-867.

References

Fig. 9: Spectra of a marble sample recorded at seven different frequencies as a function of Bo. Diagonal lines show Bo values of equal g factors. Note that peaks neither follow g factor lines nor can they be easily traced from one frequency to the next.

Object Description Date Size (cm) EPR Signal Bowl Ming Dynasty Porcelain

(kaolinite with iron impurities)

1500 w/h=15.3/7 Fe(III)

Candlestick Meissen Contemporary Böttger Red Stoneware

1920 w/h=6/12.7 Fe(III)

Jug Wedgwood Rosso Antico (ferruginous illitic clay)

1850 w/h=12.7/14.6

Fe(III)

Coin Saxon Notgeld 1920 w/h=2.2/0.2 Fe(III) Flower Pot Terracotta Clay 2010 w/h=11/10 Fe(III)

Tile White Marble 15x7.5x1 1x1x7.5

Mn(II)

Mortar & Pestle White/Gray Marble w/h=12.2/11 Mn(II)

Fig. 7: Plots of the peak-to-peak LFEPR signal (SPP) as a function of firing temperature (TF) for a) Kaolin clay, b) Fe2O3, c) RedArt clay, and d) mixtures of Kaolin clay and Fe2O3. lines are drawn to guide the eye and green boxes represent regions of ferro/ferrimagnetic

behavior.

Summary We are optimistic that LFEPR spectroscopy can be used to help study objects with cultural heritage importance. The presence or absence of spectral peaks in ceramics may provide insight into the type of clay and the TF.5,6 The ferro/ferrimagnetic features in the spectrum may provide insight into the size of the magnetic nanoparticles in the sample. Although the spectrum from Mn(II) in marble is complicated, we are hopeful that the alignment of the crystal structure will allow us to make associations with a quarry.

RedArt clay contains three spectral features which can be used to discern TF. It is not possible to reproduce the properties of RedArt by adding Fe2O3 to Kaolin. Kaolin possesses a g=4 Fe (III) peak which is a maximum at TF=700 oC. Fe2O3 is ferromagnetic at TF<500 oC and possesses the g=4 Fe(III) peak at 600<TF<1200 oC. Mixtures of Kaolin and Fe2O3 show the ferromagnetic behavior of Fe2O3 and a g=4 peak similar in size to that of Kaolin. This implies that the added iron does not substitute into the Kaolin lattice to form additional Fe(III) impurity sites, nor does it convert to Fe(III) as in Fe2O3.

Fig. 1: Images of the a) Meissen candlestick, Ming dynasty bowl, and Wedgwood rosso antico jug; b) marble mortar and pestle; and c) Saxon Notgeld coin studied by LFEPR.

100

150

200

250

300

350

400

450

500

0 5 10 15 20 25 30 35

ν (M

Hz)

Bo (mT)

Fig. 8: Mn(II) energy level diagrams. Note the large number of possible transitions at ν < 500 MHz and Bo< 30mT.

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0 5 10 15 20Bo (mT)

EPR

Sign

al ( µ

V)

Ming Bowl (#2)

Fig. 3: A 245 MHz LFEPR SC spectrum of a Ming Dynasty bowl.

-0.25-0.2

-0.15-0.1

-0.050

0.050.1

0.150.2

0.250.3

0 5 10 15 20

Bo (mT)

EPR

Sign

al ( µ

V)

Wedgewood Rosso Antico

Fig. 4: A 245 MHz LFEPR SC spectra of the Meissen candlestick holder after sample

magnetization in the reverse direction. The difference in the spectra is attributed to a

hysteresis in the magnetism of the sample.

Fig. 5: A 245 MHz LFEPR SC spectra of Wedgewood rosso antico jug.

-2.0

-1.5

-1.0

-0.5

0.0

0.5

0 5 10 15 20

Bo (mT)

EPR

Sign

al ( µ

V)

Red Clay Flower Pot

Fig. 2: A 245 MHz LFEPR SC spectrum of the red terracotta clay flower pot.

-20

-15

-10

-5

0

5

0 5 10 15 20Bo (mT)

EPR

Sign

al ( µ

V)

Meissen, Scan 1Meissen, Scan 2Meissen, Scan 3

Standards: S=5/2 Fe(III) in Ceramics Standards: S=5/2 Mn(II) in Marble To help understand the behavior of iron as a function of firing temperature, we studied the LFEPR spectra of Kaolin clay (0.7% Fe2O3), RedArt clay (7% Fe2O3), mixtures of Kaolin and Fe2O3, and Fe2O3 as a function of firing temperature (TF). Three features were observed in the 440 MHz spectra: a g=2 peak from f-centers in the clay, a g=4 peak from Fe(III), and a broad absorption from ferro/ferrimagnetism particles.

Fig. 6: Spectra of a) RedArt clay fired at 300 oC showing the broad g=4 Fe(III) and narrow g=2 f-center peaks, and b) Kaolin clay with 14% Fe2O3 showing the small g=4 Fe(III) peak

and the ferro/ferrimagnetic signal.

a b

c d

a b

The LFEPR spectrum of Mn(II) in marble is challenging to interpret.3 The high field approximation is not valid at Bo<100 mT resulting in numerous observable transitions. (See Fig. 8.)

The marble spectrum is further complicated by the partial alignment of the crystal structure due to geological processes.4 Fig. 9 displays the LFEPR spectra of a marble sample at 440, 400, 350, 300, 250, 200, and 150 MHz. a b c ♦ g = 4 peak

▲ g = 4 peak

g = 4 peak