Gromwell — 자초 (Lithospermum erythrorhizon)

What It Is

자초 (紫草, gromwell) — Lithospermum erythrorhizon — is a plant native to East Asia. Its root contains shikonin (시코닌), a naphthoquinone pigment that produces deep purple-violet to crimson colours. Shikonin is unusual among natural dyes in that it is fat-soluble and alcohol-soluble, not water-soluble — meaning standard water-based dyeing techniques do not apply.

Extraction Methods

From 장미님 워크숍 (Korean traditional materials workshop, Seoul 2026):

• Oil extraction (들기름 / 참기름): Soak dried 자초 root in perilla oil (들기름, Korean drying oil) or sesame oil (참기름, non-drying). This produces a deep purple-red oil used directly as a painting pigment. Perilla oil (들기름) is the preferred option for painting purposes as it is a drying oil and will set.
• Alcohol extraction (에탄올): Soak in high-percentage ethanol (96% or 소독용 에탄올). More efficient extraction than oil; produces a brilliant purple solution. Used for fabric dyeing when combined with a suitable mordant.
• Sodium hydroxide (수산화나트륨): Combined with oil or alcohol extraction in some traditional recipes to shift the pH and extract a different colour register from the shikonin molecule.

Colour Range

• Oil or alcohol base (neutral): Deep purple-violet
• With alkaline mordant (sodium hydroxide): Darker violet, more blue-leaning
• With acid mordant (cream of tartar): Brighter, red-leaning

Shikonin is pH-sensitive — acid conditions produce warmer red-purple; alkaline conditions produce cooler blue-violet.

In Painting

자초 oil is used as a direct paint medium — applied with a brush to paper or silk, with 아교 (animal glue) as the binding agent for opaque applications. The oil medium itself contributes to the binding. For traditional Korean painting on silk, 자초 in perilla oil can be applied as a glaze layer over lighter pigments, building depth.

In Dyeing

For textile use, 자초 alcohol extract can be applied to protein fibres (silk, wool) mordanted with alum. The colour on silk with alum produces a warm grey-purple. On wool, the result is deeper. Cotton absorbs 자초 poorly without heavy pre-treatment — animal fibres preferred.

Historical Context

자초 was a highly prized material in Korean traditional medicine (한방약) — the root was used topically for burns, inflammation, and skin conditions. The pigment overlap between dye, medicine, and painting material is characteristic of many traditional Korean natural materials. 자초 appears in historical Korean clothing documents as a prestigious purple dye, used for royal garments.

Jay's Studio Note

자초 was introduced in 장미님 워크숍 as one of the bridge materials between Korean traditional painting and natural dyeing — a root that exists in both traditions. The oil-based extraction, applied to silk in multiple thin glazes, builds a purple that is unlike any synthetic purple: slightly red in some lights, blue in others, and with a translucent depth that flat pigment cannot produce.

Related Materials

Mineral Pigments · Natural Dye · Botanical Dye Plants · Drying Oils

References

• 장미님 워크숍, Seoul 2026