Copperheads

Description of defect

Copperheads are reddish brown spots, which may vary in size from almost invisible to 3.2 mm.

Small ones are always depressed, while larger ones may be accompanied by a pulling away or curling up of the enamel.

Occurrence

This phenomena may occur at both wet & powder enameling processes.

Possible Causes

Possible causes for lumps in random order :

• Excessive iron in the pickle acid
• Poor rinsing, resulting in nickel or iron sale deposits on the metal surface
• Contaminated rinsing water after acid or nickel stage
• Rust on surface after pretreatment

• Thin enamel application
• Contamination of enamel slip with sulphates or chlorides

• Contamination of enamel shop and/or enamel furnace with chloride vapors.
• Slow drying
• Poor wetting properties of enamel