125
On all other areas of the reverse (frame, base), above the ground was applied
and polished first black lacquer (one layer) followed by red lacquer (two layers)
(figs. 32 and 33); these surfaces were subsequently decorated with black lines,
yellow fields (fig. 34), and yellow lines (meander, lower base; fig. 35).
3.2.3 BINDING MEDIA OF THE COATINGS, LACQUER, AND GROUND LAYERS
Before the analysis of the lacquer and ground layers, it was necessary for conservation
reasons to determine if, and if so, what coatings are present.
In three samples, the whitish coatings on the carved lacquer side could be
identified with GC-MS as ibota wax, an Asian insect wax. Through comparison
with a reference sample of the Japanese ibota wax
ibota-ro,23
which is used
in certain polishing processes in the lacquer technique, the results of the
analysis could be verified. The coating, which was visible under UV illumination,
was likewise identified using GC-MS: colophony with traces of shellac and
a drying oil were found. This also corresponded with the THM-Py-GC-MS
investigations performed at the Getty Conservation Institute (Michael Schilling,
Julie Chang): In a sample from the red carved lacquer side, in addition
to the lacquer components, colophony (pine resin) with traces of shellac
and cedar oil were found. The results suggest that the iboda wax is attributable
to historical care in China (as it was not common here) while the colophony
coating belongs to the later history of care in Vienna.
Asian lacquers cannot be directly analysed by GC-MS as they are insoluble.
The red lacquer of the front and black lacquer of the reverse were thus
investigated in the Conservation Science Department of the Kunsthistorisches
Museum using THM-Py-GC-MS.
The black lacquer contains urushiol (this was determined from the pyrolysis
products of the aged lacquer) and drying oils (possibly a mixture of perilla
and linseed oils). The red lacquer shows the same pyrolysis products, hence
the same binding media composition, but additionally contains cedar oil.
For comparison, samples were investigated at the Getty Conservation
Institute by the same method (THM-Py-GC-MS): The red lacquer of the
front shows a very high proportion of an oil, heat bodied tung oil, and
urushi (Chinese: daqi, Toxicodendron vernicifluum) as well as mercury sulphide
(from its pigmentation with cinnabar). In the black lacquer, perilla
oil with urushi was determined (Chinese: daqi).
23 Ibota-ro, from the Watanabe company, http://www.urushi-watanabe.net (last
accessed: 15 October 2020).
CHINESE
LACQUER SCREEN
