The Luster of Sumi — Where Does the Sheen in Black Ink Come From?

Ink Shows Its True Nature Only After It Dries

While you are writing, every ink looks glossy and black — but that shine is the water, not the ink. The real luster only appears once the paper has dried.

Write the same character twice on a large sheet, each with a different ink, and let them dry side by side. One will still return a soft light from deep within; the other loses its sheen the instant the water leaves and settles into a dull, ashen gray. You wrote the same "black," yet by morning they look like two different substances. Luster, to me, is simply the ink's ability to return light even after it has dried.

The Sheen Comes From the Glue, Not the Soot

The blackness itself comes from soot. But the luster is decided by nikawa — the animal glue that binds the soot particles to the paper. Nikawa is drawn from bone and hide, and when it dries it forms a thin, transparent film. When that film lays the soot particles down flat and smooth, the surface returns light evenly, and we read that as sheen. When the glue has thinned and the soot scatters, the light scatters too, and the same black sinks into dullness.

This is why fresh ink tends to shine and why aged ink leans away from luster toward a drier depth. When I write words of celebration, I reach for a newer lampblack ink on purpose — that glossy life suits the brightness of the occasion. On a quiet evening writing a Zen phrase, I choose an older, rested stick to keep the sheen calm. Bring out the luster, or subdue it: I have half-decided before the brush ever moves.

Grinding Can Kill the Luster

Even a good ink loses its sheen if you grind it badly. Press hard and race the stick back and forth, and the glue foams. Foamed ink dries with a fine roughness on its surface that refuses to return light. I have ruined many sheets this way — grinding in a hurry before a TikTok LIVE, the characters came out dark, yet by morning they had no luster at all, pale as if dusted with powder. Depth of black and depth of sheen are not the same thing.

Now I grind slowly, in soft circles, with the force taken out of my hand. Let the stick dissolve into the water without foaming and the luster comes willingly — five to ten minutes, until the pool on the inkstone turns heavy and pulls a thread from the brush. The stillness of the grinding hand is written straight into the shine.

Does the Paper Hold the Sheen, or Drink It?

The last variable is the paper. The same ink, ground the same way, behaves differently depending on where it lands. A tight, low-bleed paper holds the glue film at the surface, so the sheen sits up. A soft, thirsty gasenshi pulls the ink deep into its fibers, and the luster that returns to the surface stays modest.

For a work where I want the sheen to show, I choose a tightly woven paper. Once, trying to force luster from a soft sheet, I over-thickened the ink — and the black flattened and crushed, killing both the shine and the depth. Luster is never decided by the ink alone: the glue, the grinding hand, and the paper must meet. It is not something you add. It is something you take care not to kill — which is why, again today, I loosen my hand and grind.