Potassium Oxide K2O (Kalium Oxide)

Strong alkaline flux
Similar to sodium oxide except
- Slightly weaker
- Begins fluxing action earlier than sodium oxide, at about 1382°F
Predictable, stable flux
Produces bright glossy glazes
Can’t be used alone as a flux
It produces slightly stronger glaze surfaces than sodium oxide
Low viscosity and surface tension creates fluid glaze melts
High coefficient of expansion and contraction may cause crazing
Often found combined with sodium oxide, so commonly written as KNaO
Only slightly volatile at ceramic temperatures
Slightly soluble
Usually used in its insoluble forms like feldspars or slightly soluble Frits
Can be introduced to glaze recipe as a soluble like pearl ash (potassium carbonate), which can cause flashing like sodium carbonate.
Insoluble sources are
- Potash feldspars
  - Custer
  - G-200
  - K-200
  - A-3
  - Kona F-4
  - Cornwall Stone
  - plastic Vitrox
  - Volcanic ash
  - Kona A-1
  - Bell
  - Eureka
  - A-200
  - Mica
All soda feldspars have some potassium oxide
- Frits
  - P-25
  - 3110
  - 3124
- Soluble forms include pearl ash (K2CO3), potassium nitrate )saltpeter), and unwashed wood ash

Potassium Oxide K₂O (Kalium Oxide)