Features of Lac

About Lac

The term lac (also known in Japanese as shikō, 紫鉱) refers to a gelatinous, stick-like substance secreted by the male lac insect (Laccifer lacca Kerr), a member of the family Coccidae (scale insects). This insect parasitizes various host trees, particularly species within the genera Albizia (Mimosoideae), Ficus (Moraceae), and Acacia (Fabaceae), which are predominantly distributed across tropical Asia, northern Africa, and northern Australia. The secretion is produced as the insect feeds on the phloem sap of these host plants.

Lac is mainly harvested in regions such as India, Myanmar, Tibet, Thailand, and Bhutan. It was introduced to Japan during the Nara period (8th century CE), where it was employed both medicinally and as a dyestuff. Numerous historical textiles preserved in cultural heritage sites such as Hōryū-ji Temple and the Shōsōin Repository exhibit the characteristic purplish hues of shikōzome (紫鉱染), a dyeing technique utilizing lac pigment. The substance itself is still preserved in the Shōsōin under the name shikō (紫梗).

In addition to its application as a dye, the residual matter obtained after pigment extraction yields shellac, a natural thermoplastic resin. Shellac has historically served various utilitarian purposes, including as a varnish, electrical insulator, and coating agent.

About Lac dyeing

Lac dyeing is an ancient dyeing technique that has been practiced since antiquity in regions such as ancient China and the Ayutthaya Kingdom of Thailand. In Japan, it was introduced around the Nara period (8th century CE), and numerous examples of shikōzome (紫鉱染)—textiles dyed with lac pigment—remain in artifacts preserved at Hōryū-ji Temple and the Shōsōin Repository. The dye substance itself continues to be preserved in the Shōsōin under the historical name shikō (紫梗).

The coloring matter extracted from lac primarily consists of anthraquinone-type laccaic acids. These natural anthraquinone derivatives serve as the principal chromophores responsible for the characteristic hues obtained from lac dyeing. Utilizing laccaic acids, dyers are able to produce a spectrum of colors ranging from crimson (enji-iro), reddish purple, to deep purplish-black.

The method of Lac dyeing

Dyeing with lac is carried out using a mordanting method. The process begins by decocting shikō (lac sticks) in a stainless steel vessel containing water and a small amount of vinegar. After approximately 60 minutes of simmering, the decoction is filtered through cloth to separate the solid and liquid components. This extraction process is repeated three to four times to ensure maximal yield.
Through this filtration, a clear separation is achieved: the resinous component (shellac) is retained in the filtering cloth, while the aqueous extract contains the dye constituents, primarily laccaic acids (anthraquinone derivatives), which serve as the active chromophores.
When dyeing cellulose-based fibers (e.g., cotton or linen), a preliminary treatment—shitazome—is conducted using soy milk (豆汁), which acts as a proteinaceous binder to enhance dye affinity. Subsequently, an alum mordanting process is performed using the pre-mordanting method (also known as sakizome hō), wherein aluminum salts are applied to the textile prior to dye immersion. The fabric is then repeatedly immersed in the lac dye bath, a process that gradually builds up the desired hue through successive layering.

Color Difference by Mordant