Calibration and Use of the Heating Microscope for Indirect Evaluation of the Viscosity and Meltability of Archeological Glasses

Abstract

The heating microscope is a widely used instrument in many industrial applications, especially in the ceramic field, to obtain information on the sintering behavior and, indirectly, on the viscosity curve of glass. It is therefore important for the study of glass technology. Usually, heating microscopes work by taking images of the sample outline, during a preset thermal cycle, which define five characteristic temperatures corresponding to particular shapes of the specimen. The first two characteristic temperatures can also be extracted from the sintering curves provided by the instrument. In agreement with three published models, the five temperatures are associated with five viscosity values, producing the two best-fitting plots (Log 10 (g) -T). In this work, the heating microscope was calibrated using a glass with known properties, to determine the most reliable model, so that it can be applied successfully in the field of archeological science. The selected methodologies were used to analyze two opacified Roman mosaic glass tesserae excavated in Pompeii, previously characterized chemically. A Pompeiian transparent glass, sampled from a large block of base (raw) glass, and its experimental reproduction were also studied. Finally, the relationship between the opacifiers and the thermal behavior of base glass was investigated. † Member, The American Ceramic Society. *cristina.leonelli@unimore.it Hot-stage microscopy thermal run: http://youtu.be/9G0ahZoiSYw.

Glass–Ceramic Foams from Borosilicate Glass Waste

“…The two crystalline phases identified, first cristobalite already starting to show its XRD peaks at 800°C, then sodian wollastonite, are common phases in this compositional range . In particular, the wollastonite crystals developed in the present research are related to the significant CaO content in the parent glass, as observed by Agathopoulos et al .…”

“…The modification of the pellet profile was also described in more useful terms as variations of linear shrinkages versus temperature; the sintering curve has been plotted in Fig. where another commercial borosilicate glass, DURAN ® 8330, without intrinsic crystallization tendency is reported as comparison . The dilatometric curve presents the onset sintering temperature at about 670°C, little higher than T g (535°C), and presents a linear shrinkage of about 20% up to 730°C.…”

Preliminary Thermal Investigations of Calcium Antimonate Opacified White Glass Tesserae

“…There appears to be an inverse correlation between the temperature of the first thermal event and the lead concentrations, which becomes more pronounced at higher concentrations (PbO > 2 wt.%) (Figure 2). This result is in line with the workability interval measured for a raw glass from Pompeii (685-892 °C) [38]. The curves from our non-isothermal differential thermal analysis overlap perfectly with those reported in the literature for laboratory replicas of Roman calcium antimonate-opacified glasses.…”

“…All DSC measurements were carried out on approximately 20.0-25.0 mg samples against an empty Pt-Rh crucible. Being aware that the finesse of the powder affects the thermal events, we carefully ground all the specimens to achieve the same final grain size [38].…”

Thermal properties and stability of Catalan Modernist blue and green enamels

“…The temperatures related to fixed viscosity points in the softening range defined for HSM according to the German rule DIN 51730 were determined for the synthetic enamels using the HSM equipment in the Department de Mineralogia, Petrologia i Geologia Aplicada of the Geology Faculty, Universitat de Barcelona . HSM is a suitable technique to study the behaviour of glass viscosity with temperature . The synthetic glasses were ground and sieved to obtain fine (45 μm) powder which was mixed with a 1/20 solution of Elvacite in acetone and pressed into a cylinder (3 mm × 3 mm) in a uniaxial press.…”