Porcelain/Vitreous Enamel Defects

Enamel defects

Below a list of possible enamel defects, which may occure during industrial enameling, and a short description of their appearance(s)

Back-emission - Localized heavy wavy surface with in extreme cases star shapes.

Back-ionization - See back-emission

Bisque damage - Excessive area of oxidation at direct-on processes or groundcoat visible thru topcoats.

Black speck - Flat bottemed dimpel with black speck at center.

Black yellow speck - Black speck enclosed in a yellow hello

Blisters - Circular holes and bubles in surface of cooled enamel.

Boiling - See blisters

Burn off - Localised areas of rough black oxide eruptions through the enamel coating

Carbon boil - Areas of fine grey or black specks

Chipping-off - A spalting or breaking off of enameled surface in flakes of various sizes.

Contamination by soil - Tight group of blisters often surrounded by smaller unbroken blisters.

Copperhead - Reddish brown spots

Crawling - Cracking & rolling back of fired enamel

Crocodiling - Parting of the surface into a geometric pattern, like a crocodil skin.

Dimples - Slight depressions in enamel surface, which do not reach the metal substrate.

Drainlines - Lines of thick enamel extending downwards from holes, lugs and corners.

Eggshell - egg shell appearance caused by many small bubbles bursting at the surface.

Faraday cage - Thin spraying of powder enamel inside sharp corners resulting in burning off/thru during firing.

Fishscaling - Small chips or scales coming off cooled enamel.

Furnace scale - Black particles typically laying on the enamel surface.

Gasatura - See grizzle

Grease mark - Rolling back of fused enamel to reveal areas of oxidised steel, irregular formbut rounded in sha

Grizzle - Coarse leathery or textured appearance to the surface.

Gun spitting - Raised rounded flattish conical areas, typically 3 to 6 mm in diameter.

Hairlining - Group of paralel lines.

Jumping - Chipping of the first coat during firing covercoat.

Lamination - A lineair defect comprising of a line of lumps or a single elongated ridge.

Lumps - Raised rounded areas 3 to 12 mm in diameter.

Metallization - Metallic iridescence on the fired enamel surface.

Orange peel - Wavy or granular appearance, very similar to an orance skin.

Pimply surface - See eggshell

Pin holes - Slightly diffused depressions that may reach the metal substrate.

Poor adherence - Enamel chipping off due to lack of bond with substrate.

Poor powder adhesion - Applied electrostatic powder enamel falling off during product handling prior to firing

Pop-off - Small, often circular, pieces of enamel showing poor adherence to steel surface. Often leaving a

Re-boiling - See blisters

Sagging - Wavy surface patterns after firing

Shorelines - Wavy parallel lines

Spalling - Fragmentation of enamel within coating layer.

Star marks - Dark star shaped defect, whereby the enamel is slightly raised between the arms.

Substrate damage - Usually visible as dents or ridges.

Tearing - See crawling.

Water stain - Light decoloration with a round shape.

Waterlining - Wet enamel washed away during application.

How to resolve enamel defects

Resolving one of abovementioned enamel defects during an industrial manufacturing process requires a structured three steps approach.

Step I - Identify the right defect.

This may sound silly,but it is sometimes not easy to determine what is the exact defect. Incorrect identification will lead to the wrong causes & remedies.

Step II - Evaluate possible causes.

Focus your attention on the most logical ones first.

Step III - Implement appropriate remedies.

About Us

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

Our Managing Director & Owner has been personally involved in 50+ industrial porcelain enameling projects since 1984, while working respectively for Ferro (Holland) BV, Smit Ovens BV, Smit Sinus Enameling BV, Nordson Corporation and/or Ditmer Trading & Consulting BV.

We provide technical services, know-how and equipment to the porcelain (vitreous) enameling industry.