Interactions between lead glazes and bodies: research on the mode of application of the glazing mixture

HAL Id: hal-01983480

https://hal.archives-ouvertes.fr/hal-01983480

Submitted on 16 Jan 2019

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Interactions between lead glazes and bodies: research on the mode of application of the glazing mixture

Ayed Ben Amara, Max Schvoerer

To cite this version:

Ayed Ben Amara, Max Schvoerer. Interactions between lead glazes and bodies: research on the mode of application of the glazing mixture. Institución Fernando el Católico. 34th International Symposium on Archaeometry, pp.399-404, 2006, 84-7820-848-8. �hal-01983480�

Maqueta symposium archaeome. 27/3/06 16:21 Página 400

34th INTERNATIONAL SYMPOSIUM 3-7 May 2004 • Zaragoza, Spain

— The formation of a layer (interface between the glaze and the body) of small K-Pb feldspar crystallites.

We also know that the interaction depends on many parameters: the clay composition, the glaze mixture composition, the use of a single or a double firing, the firing conditions (thermal path, T° max…) (Tite et al., 1998).

2. MATERIALS AND METHODS

The study of the interface glaze/body was carried out with the binocular magnifying glass, by cathodoluminescence and scanning electron microscopy (JEOL JSM 820). In order to determine the importance of the elements diffusion between glaze and clay bodies, chemical profiles were done on cross sections. More than 100 points of EDXS analysis (Link AN10000 system) every 5 µm were plotted from the glaze to the body.

For the preparation of glazed ceramic, we chose different parameters:

— We used two different glazing mixtures: a high lead glaze with sodium (60% PbO, 25% SiO₂, 5% Al₂O₃ and 10% Na₂O) and one without sodium (70% PbO, 25% SiO₂ and 5% Al₂O₃) to evaluate the sodium effect on high-lead-content glaze.

— We used two different clay bodies: an illitic-kaolinitic noncalcareous clay (1.5 % CaO) and the same clay mixed with 25% of calcium carbonate powder (CaCO₃). In this paper the results relative to calcareous bodies only are presented (for the other case, see Ben Amara, 2002).

— We used two different thermal paths (electric kiln): a thermal path with one firing stage (heating and cooling rates: 100°C/h, temp. of plateau:

950°C, cooling time: 9.25 h) and one with three firing stages (heating and cooling rates: 100°C/h, temp. of plateau: 950, 850 and 750°C, cooling time:

11.25 h). The cooling time was more important in the second case.

Glazes were prepared in the laboratory by mixing pure analytical powders (PbS, SiO₂, Al₂O₃ and Na₂CO₃). They were applied in a water suspension on ceramic body by brushing.

3. EXPERIMENTAL DATA AND RESULTS

3.1. Study of the texture of the glaze-body interface by SEM and cathodoluminescence

In all cases, we note the presence of crystals in the glaze-body interface.

They were identified as K-Pb feldspar crystallites (with low content of calcium) or wollastonite crystals (CaSiO₃). We observed that glaze-body interface did not only correspond to the lower part of the glaze (rich in

INDEX 400

Maqueta symposium archaeome. 27/3/06 16:21 Página 403

explains the increase of interface thickness. the addition of sodium in glazing mixture increases the calcium diffusion from the body into the glaze, the calcium profiles are plotted only in the case of application of glazing mixture with sodium (fig. 2d). In the other case, the calcium content is too low (<0.3 %).

The calcium content is less important in the case of unfired body. In fact calcium is involved essentially in the formation of wollastonite crystals at the interface.

5. CONCLUSION

Observations carried out at the glaze-body interface by cathodoluminescence and scanning electron microscopy did not allow us to determine with no doubt if the glazing mixture was applied on fired or unfired bodies.

Nevertheless, we noted that the interaction is often increased by unfired bodies. Thus, the presence of an important interface zone may indicate the application of the glazing mixture on an unfired body. It was shown that a slower cooling or modification of the glazing mixture could generate an important interface zone. It was shown that some crystals are always present at the interface, independently from the nature of the bodies (fired or unfired).

In addition, this study highlights the following points:

— The cathodoluminescence allows to observe and especially to evaluate the interface thickness.

— The addition of sodium, in the carbonate form, in a lead glazing mixture increases the process of decomposition/diffusion between glaze and body and so the thickness of the glaze-body interface. A slower cooling also increases this thickness.

— The glaze composition is influenced by the elements diffusion between the glaze and its support, particularly lead and silicon. Nevertheless, the elements diffusion is not always more important in the case of unfired bodies.

REFERENCES

Ben Amara, A. (2002) Céramiques glaçurées de l’espace méditerranéen (IX^e – XVII^e siècles):

matériaux, techniques et altération (in Fr.), Ph.D Physic Thesis in archaeomaterials, Université de Bordeaux 3, 121-144.

Molera, J., Pradell, T., Salvadó, N., Vendrell-Saz, M. (2001) Interactions between clay bodies and lead glazes, J. Am. Ceram. Soc., 84, 5, 1120-28.

Müller, P. (1988) Luminescence thermostimulée de verres silicatés. Application aux verres nucléaires et archéologiques (in Fr.), Ph.D Thesis, Université de Bordeaux 3.

Schvoerer, M., Raffaillac-Desfosse, C., Bechtel, F., Ney, C., Chapoulie, R. (1991) Détection grâce à leur luminescence, de cristaux de dévitrification dans des 34th INTERNATIONAL SYMPOSIUM 3-7 May 2004 • Zaragoza, Spain

INDEX ⁴⁰³

Maqueta symposium archaeome. 27/3/06 16:21 Página 404

34th INTERNATIONAL SYMPOSIUM 3-7 May 2004 • Zaragoza, Spain

glaçures médiévales: implications technologiques, European Workshop, Université de Roma - La Sapienza, 10-12 oct. 1991, 323-342.

Tite, M.S., Freestone, I., Mason, R., Molera, J., Vendrell-Saz, M., Wood, N. (1998) Lead glazes in antiquity - Methods of production and reasons for use, Archaeometry, 40, 2, 241-260.

INDEX 404

34 ^th I NTERNATIONAL

S YMPOSIUM ON

A RCHAEOMETRY 3-7 May 2004

Zaragoza, Spain

Organising Institutions Department of Analytical Chemistry

University of Zaragoza, Spain Patrimoni-UB Group University of Barcelona, Spain

CREDITS PREFACE COLLABORATORS INDEX ARTICLES Institución «Fernando el Católico» (C.S.I.C.)

Excma. Diputación de Zaragoza

ZARAGOZA, 2006 Maqueta symposium archaeome. 25/4/06 18:04 Página 1

STANDINGCOMMITTEE M.J. Aitken (Oxford) President

M.S. Tite (Oxford) Chairman L. Barba (Mexico City)

K. T. Biro (Budapest) R. M. Farquahar (Toronto)

H. Kars (Amsterdam) Y. Maniatis (Athens) P. Meyers (Los Angeles)

A. M. Özer (Ankara) J. Pérez-Arantegui (Zaragoza)

G. A. Wagner (Heilderberg) Ch. Wang (China) S. U. Wisseman (Urbana)

•

LOCAL ORGANISING COMMITTEE Josefina Pérez-Arantegui, Chairperson

Francisco Laborda (Zaragoza) Gemma Cepriá (Zaragoza) Pedro Paracuellos (Zaragoza)

Pilar Lapuente (Zaragoza) Judit Molera (Barcelona) Lorena Merino (Barcelona) Mario Vendrell (Barcelona)

The logo on the front cover represents a piece of lustre pottery from Muel (16th century), Museum of Zaragoza. The shadow is a TEM image of Cu nanocrystals forming the lustre layer.

START

34

I

S

A

Maqueta symposium archaeome. 25/4/06 18:04 Página 2