ForMatter/Finishes/glaze/Jun blue glaze (chün opalescent)
finish_glaze_jun_blue

Jun blue glaze (chün opalescent)

glaze · translucent · Jun ware glaze, chün glaze, 钧釉, moonlight Jun

A blue-opal glaze where the color isn't from a colorant but from light scattered by tiny droplets of a separated phase suspended in the glass — physics, not pigment. Song-dynasty Jun-yao kilns (Henan, China, 11th-13th century) defined the look. Reads as moonlit sky, occasionally with copper-red flushes (Jun + copper trace = peacock or sang-de-boeuf bloom).

High-silica feldspar glaze fired to cone 9–11 in light reduction. Blue color is structural, not pigmented — phosphorus-rich glaze chemistry causes liquid-liquid phase separation on cool-down: nano-scale silicate-rich droplets (~50–250 nm) suspended in the glass scatter short-wavelength light (Mie / Tyndall scattering) and pass long-wavelength light, giving the opalescent blue. Add 0.5–2% copper oxide for the Jun-with-flush variant; reduction reduces Cu²⁺ → Cu⁰ giving sang-de-boeuf red blooms. Modern American Jun glazes (Pete Pinnell, Phil Rogers recipes) use phosphate flux additions to drive the phase separation. Hard to control reproducibly — the blue depth is a function of cooling rate.

character — structural opalescent blue, moonlit-glass register, occasionally copper-red bloomed.

Finish properties

  • leveltranslucent
  • subcategoryphase-separated opalescent feldspathic
  • applies toceramic
Pairs with materials

Second life

reversibilityzero — fired ceramic glaze cannot be unfired; the glassy layer is permanent. Damaged or chipped glaze can be re-glazed and re-fired with chemistry-compatibility planning.
blocks substrate recyclingno
renewabilitymoderate — re-glazing and re-firing is a studio-renewability path for damaged ceramic; the constraint is the original-firing temperature (the re-glaze must fire below the original).

Robin Hopper *The Ceramic Spectrum* (Krause, 2nd ed.); Daniel Rhodes *Clay and Glazes for the Potter*.