What Are Glass Container Body and Sidewall Defects?

By: Berlin Packaging Specialist

Several defects can occur during the manufacturing process of glass containers. Here are some common examples of glass body and sidewall defects, such as bird swing, cord, blisters, and seeds.

Bird Swing defect is a thin strand of glass across the inside of a container between the walls or between the wall and the bottom. It can occur in both the press-blow and blow-blow process.

Bird Swing

Internal Blisters with Thin Walls defect occurs when air bubbles get trapped inside the glass mass on the internal surface. These blisters are usually elongated and can be cracked (the surface is broken) or not cracked (with a thin skin).

Internal Blisters with Thin Walls

Stuck Ware defect occurs when two containers are attached while hot and separated while cold. This separation causes a sharp or cutting edge (rough glass edges on the side; lacerations on the contact area between the bottles).

Impossible to pack the item correctly. Risk of injury to the worker or the end user.

Stuck Ware

Burrs defect consists of sharp edges along the lines of the mold seams.

Impossible to pack the item correctly (M+). Risk of injury to the worker or the end user



Split defect is a crack which passes through the entire thickness of the glass (in any part of the container).

Breakage of the container during or after filling and packing. Risk of accidents due to bursting if used with a carbonated product.


Deformation or Deformed Item defect occurs when the container is malformed, warped, or completely sunken. Container has shape anomalies that may cause problems during filling and packing (sunken shoulder, misshapen body, etc.).

Depending on its severity, this defect may affect the filling, labeling, capacity, secondary packing, etc.

Deformation or Deformed Item

Cracked Seam defect is a fracture which usually occurs in the body of the container. It doesn’t always lead to breakage.

Breaking of the container before, during, or after its packaging.

Cracked Seam

Discontinuous Cracks defect consists of discontinuous surface cracks with one or more shiny parts (straighter crack: no protruding glass can be felt).

Breakage of the container during or after filling and packing (bursting upon handling in workplace when used for carbonated products or sparkling wine).

Discontinuous Cracks

Inclusion defect is a foreign body in the glass.

Severe risk of breakage during or after packing operations (impacts), especially with sparkling products.


Mold Seam with Pinched Glass defect occurs during the closing of the finishing mold, blocking the structure and producing a heavy seam.

The item cannot be properly packed.

Mold Seam with Pinched Glass

Impact Cone defect is an impact point from a knock that extends into the glass mass in a cone shape.

The container is not suitable for filling (serious risk of breakage).

Impact Cone

Thin Walls defect occurs when the thickness of the glass does not meet the specifications.

Risk of breakage if knocked during transport or packing.

Thin Walls

Stuck Glass on External Surface defect is an unwanted pieces of glass, which may or may not be sharp, stuck to the external surface of the container.

It may affect filling and packing.

Stuck Glass on External Surface

Blisters on the External Surface defect consists of elongated blisters that can be cracked (the surface is broken) or not cracked (thin skin) with a severity level of > 4 mm (M+), = 4 mm (M-), or < 4 mm (m).

Cracked blisters are potentially hazardous for the operator. Intact blisters of ≥ 4 mm risk breakage during bottling and handling. Dangerous with carbonated beverages. < 4 mm is considered not serious, mainly an aesthetic defect.

Blisters on the External Surface

Different Drop of Glass defect is a drop on the glass mass with radial crizzles (M+) and a drop on the external surface or the glass mass without crizzles (M-).

Radial crizzles on the glass mass may result in breakage during filling. If the external surface or the glass mass is without crizzles, there is a risk of breakage caused by thermal shocks. Aesthetic appearance of glass.

Different Drop of Glass

Light Spots defect is a markedly thinner area in the thickness of the glass which may cause fragility in the bottle.

Aesthetic problem, poor appearance, low risk of breakage.

Light Spots

Butterfly Wing Chip defect is an impact point on the body of the item (generally on the shoulder or near the bottom), usually surrounded by concentric circles giving it a scaly look (similar to a butterfly wing), and leaving the glass wall weakened.

Butterfly Wing Chip

Out of Round Item defect occurs when the container is misshapen or the circumference is imperfectly round.

Labeling can be difficult, capacity problems may arise.


Out of Round Item

Open Mark defect is a superficial and external mark with two separated, irregular rims. It can be situated on the bottom, and is normally not visible.

Body (M- / m), Bottom (m).

Open Mark

Dirt on Outside Surface defect consists of dirt deposits on the external surface (for example, oil marks), or a rough or scaly appearance, on the shoulder or on the body.

Not suitable for use for aesthetic reasons.

Dirt on Outside Surface

Hammered Appearance defect is an irregular external surface. The body looks rough and wavy, with fine undulations.

Aesthetic defect, the item is not suitable for luxury products.

Hammered Appearance

Tear defect is an open mark/crack on the glass surface.


Cord defect is a thread of a different type of glass in the mass (a thin glass ripple that can be seen through the glass).

An aesthetic defect, more serious for items to be frosted.


Mold Seam defect is a thin ridge of glass along the parting line, caused by the mold joint.

Labeling problems.

Mold Seam

Ruined Baffle defect is an excess of glass (flash) appearing whitish in color (like crushed glass), situated on the baffle line.

Ruined Baffle

Folds defect is nearly horizontal concavities on the outer surface of the container; shallow, open wrinkles.


Washboard Marks defect consists of fine horizontal ripples on the glass surface.

Washboard Marks

Orange Peel Marks defect is a rough, bumpy surface that resembles the texture of an orange.

Orange Peel Marks

Toad Skin Marks defect consists of a rough exterior surface covered with small plates. It is characterized by a grainy and dirty aspect, similar to the skin of a toad.

Toad Skin Marks

Seeds defect consists of very small gas bubbles in the glass mass, < 0.8 mm.


Fire Cracks defect is a discontinuous, open surface crack, dull in appearance, caused by local changes in temperature. Unlike a split, it is an open crack and can be felt when touching the bottle.

Fire Cracks

Oil Marks defect is a string of grey bubbles inside the glass.

Oil Marks

Experiencing defects in your glass containers? Talk to Berlin Packaging Quality Specialists today!