Color Before the Kiln
Underglazes are colored clay-based materials applied to greenware (unfired clay) or bisqueware to add color and design. Unlike regular glazes, they do not melt into a glassy surface on their own; they need a clear or translucent glaze coat on top to seal and protect the color after firing.
Underglaze vs. Glaze
Glaze: Melts in the kiln to form a glassy, waterproof surface. Applied mostly to bisqueware.
Underglaze: Stays matte and clay-like after firing unless a glaze coat is applied on top. Can be applied to greenware because it is essentially tinted clay slip: it shrinks and fires with the pot naturally.
Why Apply to Greenware?
Applying underglazes to raw (unfired) greenware has real advantages:
- Better adhesion: The underglaze soaks into the porous raw clay and bonds tightly.
- Sharper lines: On greenware, brush strokes do not bleed as much as on bisqueware.
- Layered decoration: You can apply underglaze, bisque fire, then glaze, building up layers of color and surface.
The main risk with greenware application is that raw clay is fragile. Handle freshly underglazes pots carefully.
Consistency Matters
Commercial underglazes come ready-to-use in jars. Before applying, stir thoroughly; pigments and clay particles settle to the bottom. The consistency should be like thin yogurt: fluid enough to brush smoothly but not so thin it runs.
Underglaze Setup Checklist
Before painting:
- Stir thoroughly to full suspension
- Test brush stroke on tile
- Confirm piece is dust-free
Setup quality strongly affects final color consistency.
Explore More
Underglaze color comes from metal oxide pigments, and the Wikipedia article on underglaze traces the technique from ancient Egyptian faience through Chinese blue-and-white porcelain. Many of the blue tones in underglazes rely on cobalt, a metal whose vivid blue pigments have been prized by potters for centuries.
