- Toxic metal oxide
- Usually used as an auxiliary flux in oxidizing atmospheres
- Although it is an active flux, it has a high melting point of 3587°F
- If fired in reduction it will change to metal zinc
- Will volatilize at 1742°F
- Industry used properties of zinc to flash-glaze bricks by placing zinc-filled containers through kiln and firing in reduction
- Volatilized zinc falls from chimney to kiln yard and becomes toxic dust hazard
- Zinc Oxides color response is dramatic, either good or bad
- Can heighten colors with copper and cobalt but produce dull colors when combined with chrome
- Gives strength and durability to glazes
- Improves elasticity
- May act as an opacifier
- Used in larger amounts to produce crystalline effects
- Has medium viscosity and surface tension, which make it somewhat prone to crawling, exacerbated by high initial shrinkage of raw zinc oxide during firing
- Often calcined zinc oxide is used to reduce the initial shrinkage
- Has low expansion and contraction rate, so it can reduce crazing
- Keep in mind it can contain lead impurities
- Insoluble sources are zinc oxide and calcined zinc oxide