Barcelona, September 17th, 2021. The following material is a summary of the main concepts presented during the conference cycle Raden technique given by the Master Tatsuya Matsumoto with the collaboration of Mingxin Ma. Conferences that were held on the 5th of June and the 3rd of July of 2021, as part of the project “Urushi knowledge as contribution to the Sustainable Development Goals. An exchange between Japan and Catalonia as an example of promotion of cultural diversity, implementation of the goal 4.7 and the preservation of the cultural property and world heritage” coordinated by the Cultural Association for the Knowledge of the lacquer art (Catalonia) and funded by the JEC Fund Grant (Osaka, Japan).


Decorative technique in which pieces of shells are cut into various shapes and inlaid in urushi or wooden substrates. Urushi is applied in layers and abraded until it conceals the shells to make a flat surface. We can also find art works in which the shell was barely covered and kept raised above the urushi ground. 

 There are three types of Raden:

·RadenShell piecesinlaid into urushi.

·Kiji Raden – Shell pieces directly inlaid in the wood substrate.

·Kiseki (Jushiji) and Raden – Shells and precious stones are inlaid into urushi.

Raden is also classified according to its thickness:

Atsugai Raden – Thick 0.5 to 1 mm.

Daitai-bori is the name of the technique in which the substrate is carved to inlay thick shell pieces.

Usugai Raden – Thin, less than 0.5mm.

Kinds of shells commonly used:


Yakogai – Green turban, marbled turban (traditionally collected in Okinawa)

Awabigai – Abalone

Shirochogai – Pinctada maxima

Kurochogai – Black Pinctada maxima

Mexican Abalone

Taimai – Tortoise shell

Chōgai – Pearl oyster

* Tamamushi-gai is referred to as abalone that color is only green and blue in very small pieces.


 Taimai (tortoise shell), amber, rock crystal, precious and semiprecious stones are also used.

Raden cut-out and gluing

Threat saw with a 3/0 to 6/0 saw blade is commonly used. The precision sanding is made with metal files. Carving knives are used to engrave the substrate, the urushi coatings and the shell surface.

Thin raden can be moistened to facilitate cutting.

Nikawa (animal glue) and Rose-urushi (mix raw-urushi and Roirourushi) are the most used adhesives.

Nigai: The traditional method for taking mother-of-pearl from Green turban, by boiling them in sea water for several hours.

Pieces studied in both conferences

1.- Five stringed biwa lute of red sandal wood, with mother-of-pearl inlay. Shosōin Treasure.


2.- Raden mirror, eight-lobed bronze mirror, decorated on the back with mother-of-pearl inlay. Shosōin Treasure.


3.- Box with fuseryō design in mother-of-pearl inlay and maki-e, 13th century Kamakura period, National Treasure, Suntory Museum of Art.


4.- Ornamental coffer with flower and bird design in maki-e and raden techniques. Museum Für Ostasiatische Kunst, Kōln.


5.- Cabinet with landscape design in maki-e decoration. Museo Nacional de Artes Decorativas, Madrid (only available in Spanish).


6.- Container in the shape of a crane, 19th century, Rijksmuseum, Amsterdam.


Ornamental styles analyzed

  • Nagasaki Raden, 19th century.
  • Chinese mother of pearl lacquerware, Yuan Dynasty 1271-1368.
  • Goryeo Raden, Dynasty of Korea, 12th century.
  • Ryukyu Raden.

Raden techniques analyzed in the previous pieces

Fusesaishiki method

·To apply gold, platinum, silver foil or color (pigments or color urushi) to the back of the shell so it can be seen through it once placed.

·To glue the metal leaf to the shell, the back of shell is covered by a thin coat of urushi which is instantly wiped, leaving just a thin layer as adhesive.  Once it is dry, the shell can be cut according to the desired design and glued to the surface of the project.

·When the reverse of the shell is painted, vivid colors are used. Syu urushi (red lacquer) is often used.

·Pieces of shell are cut into different shapes and pasted (with rice glue diluted in water) on a sheet of paper following a design. Then the back of the design is coated with urushi and pressed into the already prepared surface of the project.

·When it is dry, the paper is removed with warm water, coated and filled with roiro urushi.  

·Two methods to reveal shell after coated with urushi:

Togidashi method – grinded the whole surface with charcoal or polishing stone.

Hagidashi method – use a spatula or a knife to remove the urushi on the shell.

* Warigai method – break a piece of shell to make cracks and use it as texture for the pattern.

 Raden restoration. Cleaning and consolidation.

After the preliminary investigation and documentation in some conservation cases, these are the general steps followed.


·Brushing off dust.

·Remove dirt with cotton cloth slightly moistened with purified water.

·Dirt that is difficult to remove, use ethanol diluted with purified water.


The detached shell pieces protruding from the surface are impregnated with ethanol, lowering the surface tension, and then impregnated with Nikawa (animal glue) with a few drops of ethanol. The excess glue is wiped off, also Gampi paper is placed on the raden to absorb the glue excess and to protect the shell, finally, the shell pieces are press stabilized by means of the Shinbari technique, in which the piece to be consolidated is placed inside a wood frame that allows to fit bamboo sticks (and other types of wood or carbon fiber sticks) by exerting pressure on specific areas.  It is important to place over the raden acrylic plates during the procedure, since the Shinbari technique requires a homogeneous pressure.

It is also important to create a mold that will act as a counterweight inside pieces with thin walls or pieces that can suffer damage due to the pressure in the Shinbari frame.

Diluted mugi-urushi (adhesive made of the mixture of raw urushi with wheat flour, that has been previously kneaded with water into a dough) can be used to consolidate thick raden, since being thick it is not translucent and does not modify its color. Mugi-urushi can be diluted with turpentine. Detached urushi coating film around the shell pieces and rims can be treated with diluted mugi-urushi as well. Extra care must be taken not to affect the color of the raden pieces.

This activity is one of the activities for the spreading of this kind of art organised by ACCAL within the programme of activities carried out thanks to the support of the JEC FUND GRANT.