" It is a paradox of the porcelain enameling industry
that it is less expensive to produce good ware
than to produce an equal quantity of bad ware."


Beneath you will find a comprehensive outline of major enamel defects and their possible causes,
which is mend to simplify troubleshoothing your enameling operation.

Defect	Appearance	Possible causes
Back-ionisation	Localised heavy orange peel	+ Excessive film thickness + Too high gun voltage + Guns too close to workpiece + Low relative humidity of ambient + Poor earthing + High powder resistivity + No AFC used
Black specks	Blisters or circular holes	+ Iron contamination + Poor steel quality + Over pickling + Contamination with organic materials + High humidity in furnace + Incompetible enamel combination (2c/1f processes)
Chrome contamination	Black specks enclosed in a yellow halo	+ Scaling from firing tools + Scaling from furnace furniture
Dimples	Slight depressions in enamel surface	+ Oil or water spots from compressed air line + Contamination by dust from ambient + Contamination by sulphate depositions
Faraday cage	Burning off due to thin spraying in the angle of sharp corners	+ Too high charging potential (kV) + Poor product design + Poor particle size distribution of enamel + Excessive amounts of reclaimed enamel
Gun spitting	Raised areas, sometimes discoloured	+ Powder accumulation around gun tip + Poorly maintained guns + Using compressed air with too high dewpoint
Poor powder adhesion	Localised fall off of powder	+ Poor powder charging + Too many large powder particles + Poor powder storage + Too low charging voltage (kV) + Excessive gun-to-ware distance + Excessive powder recycling + Vibrations / shocks + Intervall between powder application and firing

For more detailed information, about enamel defects, I would refer to the excellent manuals of the American and English Enamel Associations :

- Atlas of enamel defects, VEI, 1996
- Technical manuals, PEI, 1997

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