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sherds of
yohen tenmoku

 

Research-outline for laboratory and instrumental analyses of the sherds of fragmentary Yohen tenmoku 1.12.02


David V. Hill, Philippe Sciau, and Tiequan Zhu


Background (abstract)


Tenmoku ceramics are physically complex objects whose appearance is the result of the interactions at three different zones; the ceramic body, a transition zone at the glaze-body interface and the glaze. The ceramic bodies are composed of a high alumina-silica clay containing additives that are sintered into a stable support for the glaze. The glaze has less alumina and more flux that lowers the melting temperature to produce the glassy phase. The glaze is a glass that retains many natural flaws such as gas –bubble inclusions, crystal participates, undissolved inclusions1, and variegated colors based on the uneven distribution of iron or other coloring elements in different valence states. Depending on the glaze composition conditions of liquid-liquid immiscibility allows for the growth of crystalline structures within the glaze.


Through the control of kiln temperature, firing duration, kiln atmosphere, and the composition of the glaze, the potter can produce distinctive decorative features such as oil-spot, hare’s fur and partridge-feather as well as the growth of crystals or bubbles at the glaze-body interface along with diverse hues most commonly brown or black (Farrell 1995). Other colors have been identified in ancient glazes including an iridescent coating derived from a silica coating of the underlying glaze (Jianxing et al. 1995; Minn 1995).


ASET Holdings is represented by several types of tenmoku, including several types of Yohen tenmoku. One of the types of Yohen tenmoku in ASET Holdings is characterized by a thick black glaze on a coarse textured ceramic body2. The clay body is silvery, compact and dense in appearance with extensive mineral inclusions. This includes blackish minerals mottling the coarse greyish clay body; they present hues ranging from dark brown to black. Extensive whitish inclusions are also present. The exterior is decorated with splashes with light bluish to white glaze formations with black-colored crazing with thin films of iridescent interface over a black slip sealed under a transparent glaze. The interior of the vessel incorporates splashes of white, blue and red glaze with a thin film of iridescent interface over a black slip sealed under a transparent glaze.


The bottom of the bowl is decorated with a massive emerald green-transparent layer of glass. The green layer is further framed by a beryl-colored, glaze formation with a complex crystalline structure made of prismatic to tabular crystals, what a remarkable with a mineral-like texture and appearance.


Silvery white crystals are present at the glaze-body interface. Sparse silvery white crystals are also present within the emerald green-transparent layer just below the exterior surface of the green crystalline glaze formation.


The type of the Yohen tenmoku vessels in ASET Holdings corresponds to an exceedingly rare Yohen tenmoku type3, of which three are known to the present authors: a fragmentary Yohen Tenmoku bowl, recently recovered from Hangzhou, Zhejiang Province, China; two similar bowls, both in Japan in the Seikado Bunko Art Museum, Setagaya, and the Fujita Art Museum, Jiangxi4 .


Objectives & aim


The objective of the proposed study is, using a similar laboratory and instrumental approach as: PHASE I Sample Groups 1.0–8.0 Research Protocol. Topic II, to undertake detailed research investigations on the sources of production and origins of raw materials of the present type of tenmoku, as represented by sherds of fragmentary Yohen tenmoku 21.12.02. The aim is to verify to the extent that the (i) body composition is consistent with the Yohen tenmoku bowl recovered from Hangzhou. Besides determining: (ii) the composition and formation process of the glaze, it is important to conduct research on (iii) coloring processes and chromogenic mechanisms of the glaze (Sciau 2015); (iv) the nature of the degradation processes and deterioration mechanisms of the glaze and the ceramic body, mineral alterations and pseudomorphic replacements.


Detailed descriptions of the primary components or phases of the glaze: (a) the homogeneous glass phase, (b) crystallization phase, and (c) liquid-liquid phase separation should be also made (Kingery et al., 1983; Yang et al., 2009;).


Silvery white crystals are present in the glass at the glaze-body interface. Sparse silvery white crystals are also present in the glass just below the exterior surface of the green glass.


A. Non-invasive analysis: (i) Microscopic analysis of ceramic glaze and underglaze;(ii) Ramen spectroscopy of ceramic body (for comparison withinvasive analysis);(iii) Portable XRF of ceramic body (for comparison with invasiveanalysis);(iv) PIXE or any combination of synchrotronradiation-based μ-XRF, μ- XRD, μ-XANES to obtain high resolutiondata for research on the composition and formation process of theglaze, its colorant processes (Sciau 2015); as well as the degradationprocesses and deterioration mechanisms of the glaze and the ceramicbody by the mineral alterations and pseudomorphic replacements ofkaolin-based clay body (Merino et al. 1993, Yang 2012).


B. Invasive analysis (oriented towards sherds):(i) thin-section petrology(ii) Electron microprobe analysis of ceramic paste;(iii) XRMF (X-ray μ-fluorescence) analysis of ceramic body, glazecomposition, microcrystalline structures (Sciau et al. 2015); (iv) Micro-XRF imaging of the distribution of iron phases in theglaze.(Sciau et al. 2015); (v) Electron microprobe and XRD analysis of iron-rich inclusionspresent in the fired ceramic body (Merino et al. 1993);(vi) PIXE analysis of phase boundaries in weathered kaolinites (Merino et al 1993) and the glaze.


References Cited


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1 To which extent gas trapped in bubbles formed in the glaze, during the firing process, may play a significant role in the glaze resultant reflective index is an important question, which yet to be investigated.


2 Numerous copies and forgeries of the type are known. Like the ‘Chicken Cup’ the type has been extensively copied and imitated; and its unique composition of the glaze was likely to be characteristic during its period of maufacture.


3 Numerous copies and forgeries of Chinese glazed ceramics are well known. The ‘Chicken Cup’ from the Ming dynasty has been extensively copied and imitated. However, the glaze composition of original “Chicken Cups” should be unique and distinctive.


4 Bibliography needed.


5 To which extent these phases include un-melted quartz or residuals particles.