Bidoro: The Glass-Green Drips on Bizen Pottery
Bidoro is natural ash glaze in which ash settled thickly during a wood firing has melted and pooled in a vivid, glassy green.
The name comes from Portuguese vidro, glass. The word entered Japan in the 16th century and became, just as it was, the name of a kiln effect.
Where ash gathered and ran during a long firing, translucent green pooling and rivulets appear. It is often seen on Iga ware and Shigaraki ware, and in tea ceramics it is loved as one of the most beautiful things a kiln produces.
Goma against bidoro
The same melted-ash natural glaze takes different names according to quantity.
| Name | Amount of ash | How it looks |
|---|---|---|
| Goma (sesame) | Falling thinly, in specks | Small grains as if sesame were sprinkled. Common on Bizen |
| Bidoro | Settling thickly | Melts and runs into translucent green pooling |
| Tamadare | Thicker still, running down | Green droplets set in place as they hang |
Places where ash falls heavily are only a few limited positions inside a kiln: the side near the stoking port, the upper faces along the flame path. Makers aim to place pieces there, but they cannot decide where or how much will gather.
What to look at
Bidoro shows its quality against the light. Thickly pooled areas sink to a deep green, thin areas glow yellow-green. And at the end of a run, a small bead has sometimes formed where the drip stopped.
There is also always bare clay around bidoro. Glassy green and dry earth. That gap is the scenery of unglazed pottery, and exactly what keshiki sets out to read.
Using bidoro pieces
Bidoro is glassy, but the piece beneath it is absorbent stoneware. Basically it needs the same care as any stoneware.
Doing medome at the start prevents cooking oils and odours from soaking in. Depending on how the bidoro has settled and how hard the piece was fired, the surface may also carry fine air holes or crazing. After use, wash gently by hand with detergent and dry thoroughly somewhere with good airflow before putting it away. Avoiding the dishwasher and microwave is safest.
Related terms and guides
Related terms
- Shizen-yu: Natural Ash Glaze Explained
- Yakishime: Unglazed Pottery Fired to Its Limit
- Anagama: Inside Japan's Oldest Wood-Fired Kiln
- Hidasuki: The Red Straw Marks on Bizen Pottery
- Medome: How to Seal Unglazed Pottery Before First Use
- Japanese Pottery Glossary | Terms, Techniques & Kilns
Read further
- Keshiki: How to Read the 'Landscape' on a Pot
- Shigaraki Ware: Why Its Clay Sparkles After 1,200 Years
- Iga Ware: Fire, Ash and the Beauty of Rough Clay
- How to Care for Japanese Ceramics: A Practical Guide
Pieces available at Nokaze
Look at how the green runs
Deep green where it pooled thickly, yellow-green where it thinned. Bidoro runs differently on every piece. Nokaze introduces unglazed stoneware.
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New to Japanese pottery? Start here — its history, how pottery differs from porcelain, the clays and glazes behind each style, and how to care for a piece. → Japanese Pottery: The Complete Guide