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Ditmer Trading & Consulting BV

Professional Services & Supplies

Powder Enameling Defects
Typical appearances and possible causes

" 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 troubleshooting your enameling operation.

Defect Appearance Possible causes
Back-ionization Localized heavy orange peel + Excessive film thickness
+ Too high gun voltage
+ Guns too close to work piece
+ Low relative humidity of ambient
+ Poor earthing
+ High powder receptivity
+ No AFC used
Black specks Blisters or circular holes + Iron contamination
+ Poor steel quality
+ Over pickling
+ Contamination with organic materials
+ High humidity in furnace
+ Incompatible 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 discolored
+ Powder accumulation around gun tip
+ Poorly maintained guns
+ Using compressed air with too high dew point
Poor powder adhesion Localized 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
+ Interval 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

and the reference book by Silvano Pagliuca and William D. Faust :

- Porcelain (Vitreous) Enamels and industrial enamelling processes, 2011

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About Us

Ditmer Trading & Consulting BV is a family owned company, which was founded by Ronald Ditmer in 2007.

We are specialized in providing worldwide professional services & supplies to the porcelain (vitreous) enameling & powdercoating industry.

Company details

Ditmer Trading & Consulting BV
Palissander 141
3315MP Dordrecht
The Netherlands

Phone : +31-78-6169877
e-mail :


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