Analysis of Japanese lacquer

A sample as it appeared after being embedded in polyester resin and polished as a cross section.

A sample as it appeared after being embedded in polyester resin and polished as a cross section.

Cross section showing the full stratigraphy of the Mazarin Chest lacquer, including all the foundation layers down to the nuno-kise.

Cross section showing the full stratigraphy of the Mazarin Chest lacquer, including all the foundation layers down to the nuno-kise

This is a cross section of one of the samples of lacquer, viewed under a microscope using ultraviolet light. From the bottom, it shows a layer of indigo dyed textile (nuno-kise), then four foundation layers (shitaji) made from a mixture of clay and lacquer. The topmost of these foundation layers was abraded flat, and then a carbon layer was applied. A finely divided foundation layer (shitaji) and more carbon were then used, before finishing the surface with dark and glossy urushi lacquer.

Cross section showing the upper layers of a sample from a maki-e area.

Cross section showing the upper layers of a sample from a maki-e area

This cross section shows the upper layers of the lacquer on the Mazarin Chest, viewed under normal light. A second layer of carbon was applied on top of the fine upper foundation layer. Two series of layers of lacquer were applied, with another layer of carbon between them, to create the black lacquer of the background. Decoration was applied on top, in this case a maki-e finish, obtained by sprinkling gold dust on a wet layer made of a mixture of lacquer and the red pigment cinnabar (mercury (II) sulphide, HgS).

Upper lacquer layers in a cross section viewed under ultraviolet light (1) and thin section viewed in transmitted light, showing the extent of light-damage to the surface of the lacquer (2).

Upper lacquer layers in a cross section viewed under ultraviolet light (1) and thin section viewed in transmitted light, showing the extent of light-damage to the surface of the lacquer (2)

Optical microscopy was particularly useful for assessing the degree of degradation of the lacquer surface, by helping to understand the depth of the microcracks in the surface of the urushi.  This image shows two samples of degraded lacquer, the first viewed under ultraviolet light and displaying a few thin vertical cracks, the second viewed under visible light and displaying severe cracks in the top lacquer layer but not in the second. The thin carbon layer between the topmost lacquer layers (a very unusual occurrence) acted as a stress release layer, which prevented light induced micro-cracks from propagating through the layers below, but also made the uppermost lacquer layer exceptionally vulnerable to loss during cleaning.

Hyomon decoration on the geometric border on the sides, front and top of the chest.

Hyomon decoration on the geometric border on the sides, front and top of the chest

Hyomon decoration from the geometric border with fine lines of tsukegaki applied around all edges of the metal foil. This technique is both decorative and practical - while it remains intact, it covers and protects the edges of the foil.

Cross section showing the upper layers of lacquer and hyomon sample.

Cross section showing the upper layers of lacquer and hyomon sample

This cross section shows the layer structure of the metal foil (hyomon and kanagai) decoration. The lowest carbon layer and fine foundation layer can be seen (though the other carbon layers are not visible). A layer of lacquer was applied and, once dried, deer glue was used to adhere the silver foil decoration. A second layer of lacquer was then applied. Finally, a fine line of decoration (tsukegaki) was added to the edges of the foil - gold powder was sprinkled onto a still-wet mixture of vermilion and lacquer.

XRF spectrum from a silvery area. Silver is the predominant element, but gold

XRF spectrum from a silvery area. Silver is the predominant element, but gold, mercury, copper, lead and iron are also present

XRF analysis
Many areas of the surface decoration of the chest were analysis by X-ray fluorescence (XRF), a technique that reveals the elements present on the surface of an object. This showed that gold and silver, alone or in combination, were used for all the maki-e and hyomon areas.  The subtle variations of colour and texture of the surface were obtained by mixing variable amounts of the precious metals in powder form. Occasionally, mercury from the cinnabar present under the maki-e can be also seen, as well as iron from the iron-oxide-containing shitaji foundation layers.