Analysis of Various Defects of Enamel Products

There are many reasons for the quality defects of enamel products, and various defects need to be analyzed separately. Today, I will analyze various defects in detail with you. There are common quality defects and uncommon ones, such as bubbles, scorching, peeling off porcelain, copper heads, porcelain layer tearing, silk lines, bubble hairline (chicken feet), boiling, water lines, pinholes and many more. The causes of various defects will be introduced below.


1. Bubbles

The bubbles are air bubbles in the enamel layer after cooling, and the reasons can be attributed to:

Poor quality of steel plate

The steel plate has scratches and damages

Excessive pretreatment pickling

Improper firing control

The enamel slurry is coated too thickly and cannot be burnt through

There are impurities in the enamel frit

Insufficient firing of the ground coat

Excessive water vapor in the kiln causes hydrogen pollution


2. Scorched

The primer is not evenly coated

The ground coat is too soft and there is too little quartz

The firing temperature is too high or the time is too long


3. Remove the piece and remove the porcelain

The flaking is that when the enamel is cooled or after cooling, the enamel cracks and peels off. Stripping often penetrates the entire enamel layer and reaches the steel surface.


If there is no problem with the quality of the steel itself, most of the stripping is caused by too thick enamel coating, external mechanical stress, or the surface of the steel plate is not clean. If the expansion coefficient of the enamel is too low, pressure during cooling will also deepen the peeling.


Some of the steel plates are improperly stamped and processed, resulting in micro-cavities on the surface of the steel plates, and the enamel cracks and peels off after 3 to 5 days after applying the enamel.


4. Copper head (copper spot)

The copper head is the reddish-brown spots on the ground coat, which is caused by the oxidation of iron in the enamel slurry.

The pretreatment of steel plate is not cleaned up

Excessive pickling

Excessive neutralizer

Pollution of enamel and enamel slurry

The ground coat is too thin

Drying is too slow

The ground coat contains iron

It rusts after being placed for too long before glazing

Incorrect melting degree

Use inappropriate steel plate


5. Tearing and bursting

The enamel layer is cracked (slightly) in the form of a network, often penetrating the entire enamel layer.

The viscosity of the enamel slurry is too small

Poor drying prematurely or overheating

Undried firing

Insufficient drying strength

Apply enamel on contaminated products

The enamel slurry is applied too thickly

The green body moves when drying, and the part is bent during firing

Apply with low specific gravity enamel slurry

Use aged enamel slurry and frit to dissolve it into alkaline.