Glass Packaging Defects and How to Identify Them

Defects in the construction of your glass bottles and jars are relatively rarely seen these days, with the huge improvements in quality control at glass manufacturing plants causing defective items to be immediately rejected and recycled right on the manufacturing line. However, when you do come across something, how do you identify it clearly using industry-recognised terminology, so that you can clearly explain the issue to your glass manufacturer?

Let's start with one or two of the lesser-known terms relating to the anatomy of a bottle or jar, to assist in easily identifying which part you mean:

finish: the very top of the container (above the neck ring parting line, including the top sealing surface, the neck bore, and the neck bead/collar/ring).

body: (or sidewall) the main part of the container.

insweep: the curve between the body and the bottom of the container.

punt: (or push-up) the centre of the bottom of the container which is raised up, so that the outside edge of the bottom can provide a firm base and the container sits straight.

With these terms covered, we're going to move on to a broad selection of the better-known issues that can arise with glass primary packaging such as bottles and jars. Without knowing these terms, some of these glass manufacturing problems can be surprisingly complex to describe!

Diagram showing a Spike - a type of defect occurring in glass packaging

Spike

A projection of glass extending upwards from the bottom on the inside of the jar or bottle.


Diagram showing a Bird Swing - a type of defect occurring in glass packaging

Bird Swing

A thin strand of glass across the inside of a container either between the walls or between the wall and the bottom.​

Diagram showing a Neck Spike - a type of defect occurring in glass packaging

Neck Spike

A small projection of glass at the finish or irregular wall thickness with a crater-like depression in the center, whose edges are in relief and can chip easily.​

Diagram showing an Internal Fragment - a type of defect occurring in glass packaging

Internal Fragment

A fragment of glass of any size, attached or loose, inside the container.​

Diagram showing Internal Blisters - a type of defect occurring in glass packaging

Internal Blisters

Air bubbles trapped inside the glass mass to be found on the internal surface.



Diagram showing an Overpress - a type of defect occurring in glass packaging

Overpress

A finish which has excessive glass projecting upward from the inside edge of the finish. This is a critical defect in all types of finish.​

Diagram showing Stuckware - a type of defect occurring in glass packaging

Stuckware

Two articles 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).​

Diagram showing Burrs - a type of defect occurring in glass packaging

Burrs

Sharp edges along the lines of the mould seams.​

Diagram showing a Cracked Seam - a type of defect occurring in glass packaging

Cracked Seam

A fracture which usually occurs in the body of the article. It doesn’t always cause breakage.


Diagram showing Discontinuous Cracks - a type of defect occurring in glass packaging

Discontinuous Cracks

Discontinuous surface cracks with one or more shiny parts (straighter crack: no protruding glass can be felt).​

Diagram showing an Inclusion - a type of defect occurring in glass packaging

Inclusion

Foreign body in the glass.





Diagram showing Mould Seam with Pinched - a type of defect occurring in glass packaging

Mould Seam with Pinched

When the finishing mold closes it blocks the structure and produces a heavy seam.​

Diagram showing an Unfilled Finish - a type of defect occurring in glass packaging

Unfilled Finish

The finish is not completely regular; the thread profile has not been formed properly. There is glass missing from the top surface.

Diagram showing a Split Finish - a type of defect occurring in glass packaging

Split Finish

A small vertical crack starting at the top of the finish and going downwards. This defect is difficult to detect because it does not reflect light.​

Diagram showing an Impact Cone - a type of defect occurring in glass packaging

Impact Cone

Impact point from a knock that extends into the glass mass in a cone shape.



Diagram showing Internal Marks - a type of defect occurring in glass packaging

Internal Marks

Internal marks of any kind (water, dust, cardboard, grease etc.) which cannot be removed by the preliminary washing procedure.​

Diagram showing Missing or Incorrect Engravings - a type of defect occurring in glass packaging

Engravings (Missing or Incorrect)

Any missing or incorrect engravings meaning that it is not possible to sell the article (capacity indication, spelling mistakes, etc.).​

Diagram showing Excessive Hot End Surface - a type of defect occurring in glass packaging

Excessive Hot End Surface

Tin: visible iridescence on the empty article, more obvious when filled; Titanium: barely visible or invisible mark on empty article, it gives the product a dark/purplish color (DE).​

Diagram showing No Cold End Surface Treatment - a type of defect occurring in glass packaging

No Cold End Surface Treatment

Excessive treatment causes slippery bottles, no treatment causes friction on contact between containers.


Diagram showing a Choked Neck - a type of defect occurring in glass packaging

Choked Neck

Excess of glass in the neck which partially or completely obstructs the bore and doesn’t allow the filling tube to be introduced.

Diagram showing a Hollow Neck - a type of defect occurring in glass packaging

Hollow Neck

Depression in the thickness of the glass in the neck of a bottle.​





Diagram showing Thin Walls - a type of defect occurring in glass packaging

Thin Walls

The thickness of the glass does not meet the specifications.



Diagram showing a Bent Neck - a type of defect occurring in glass packaging

Bent Neck

The vertical axis of the neck is at an angle to the vertical axis of the body.



Diagram showing a Flash - a type of defect occurring in glass packaging

Flash

A projection of glass > 0.5 mm that runs around the seam between the finishing mold and bottom plate, due to incorrect join between the mold and the bottom plate leading to protruding glass.

Diagram showing Orientation Marks (non-conforming) - a type of defect occurring in glass packaging

Orientation Marks (non-conforming)

The marks do not conform to the drawing or are missing.​




Diagram showing Stuck Glass - a type of defect occurring in glass packaging

Stuck Glass

Unwanted pieces of glass, which may or may not be sharp, stuck to the external surface of the item.

Diagram showing External Blisters - a type of defect occurring in glass packaging

External Blisters

Usually elongated, they may be: Cracked (the outer surface is broken) or Not Cracked (but with a thin skin).


Diagram showing a Chipped Finish - a type of defect occurring in glass packaging

Chipped Finish

A small fragment of glass has been chipped off the finish (scratched), sometimes not completely detached.

Diagram showing Checks on the Finish - a type of defect occurring in glass packaging

Checks on the Finish

Horizontal Threads – small crack running from the top of the finish in a downward direction. It can be seen by looking at the light reflection while turning the bottle.

Diagram showing Different Drop - a type of defect occurring in glass packaging

Different Drop

On the glass mass with radial crizzles, or on the external surface of the glass mass without crizzles.​

Diagram showing a Lump - a type of defect occurring in glass packaging

Lump

Small glass protuberance on top surface of the finish, only in one point of the finish. <0.3mm not significant, ≥ 0.3 mm: defective.

Diagram showing a Chipped Finish - a type of defect occurring in glass packaging

Offset Finish

When the offset is up to or more than 0.3 mm.



Diagram showing a Shoulder Check - a type of defect occurring in glass packaging

Shoulder Check

Beginning of a crack that does not pass through the entire thickness of the glass (usually in a straight line).


Diagram showing a Sunken or Deformed Punt - a type of defect occurring in glass packaging

Sunken or Deformed Punt

Slough or deformation of glass in the punt, making the bottle below capacity.​




Diagram showing a Baffle Mark - a type of defect occurring in glass packaging

Baffle Mark

Imprint on the bottom due to poor fit between the baffle plate and the blank mold.



Diagram showing an Out of Round Item - a type of defect occurring in glass packaging

Out of Round Item

The article is misshapen, or the circumference is imperfectly round.



Diagram showing a Deformed Item - a type of defect occurring in glass packaging

Deformed Item

An item that, while corresponding to the shape in the technical drawing, has anomalies in the shape that may cause problems during filling and packing (sunken shoulder, misshapen body, etc.).

Diagram showing an Out of Vertical Finish - a type of defect occurring in glass packaging

Out of Vertical Finish

The finish axis is not aligned with the body, even though the finish and body axes are parallel and vertical.​

Diagram showing a Bulged Finish - a type of defect occurring in glass packaging

Bulged Finish

Protuberance on the inside of the finish which can affect the finish during uncorking; no risk of scratching.


Diagram showing Light Spots - a type of defect occurring in glass packaging

Light Spots

A markedly thinner area in the thickness of the glass which may cause fragility in the bottle.


Diagram showing a Neck Lump - a type of defect occurring in glass packaging

Neck Lump

Round protuberance inside the neck, not fragile.​
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Diagram showing a Butterfly Wing Chip - a type of defect occurring in glass packaging

Butterfly Wing Chip

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.

Diagram showing a Shell Shaped Chip - a type of defect occurring in glass packaging

Shell Shaped Chip

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 shell) and leaving the glass wall weakened.​

Diagram showing an Open Mark - a type of defect occurring in glass packaging

Open Mark

Superficial and external mark with two separated, irregular rims. It can be situated on the bottom, and is normally not visible.


Diagram showing Shear Marks - a type of defect occurring in glass packaging

Shear Marks

A mark on the surface of the bottle caused by the shears.​
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Diagram showing Checks Under Finish - a type of defect occurring in glass packaging

Checks Under Finish

A surface crack under the finish, at the join between the finish mould and the preparatory mould.

Diagram showing a Shifted Bottom Plate - a type of defect occurring in glass packaging

Shifted Bottom Plate

The whole body of the article has shifted at one side by ≥ 1mm, the bottom axis is not aligned with the body axis.

Diagram showing an Inclined Bottom Plate - a type of defect occurring in glass packaging

Inclined Bottom Plate

The bottom is not completely perpendicular to the axis of the bottle. It may be inclined to one side or wavy.

Diagram showing Deformed Bottom - a type of defect occurring in glass packaging

Deformed Bottom

The center of the bottom is lower than the external rim of the bottom. ​
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Diagram showing a Bent Finish - a type of defect occurring in glass packaging

Bent Finish

The vertical axis of the finish is at an angle to the vertical axis of body.



Diagram showing Dirt on Outside Surface - a type of defect occurring in glass packaging

Dirt on Outside Surface

Article has dirt deposits on the external surface (for example oil marks), or a rough or scaly appearance, on the shoulder or on the body.

Diagram showing a Hammered Appearance - a type of defect occurring in glass packaging

Hammered Appearance

Irregular external surface. The body looks rough and wavy, with fine undulations.



Diagram showing a Tear - a type of defect occurring in glass packaging

Tear

An open mark/crack on the glass surface.​
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Diagram showing a Cord - a type of defect occurring in glass packaging

Cord

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


Diagram showing a Mould Seam - a type of defect occurring in glass packaging

Mould Seam

A thin ridge of glass along the parting line, caused by the mould joint.




Diagram showing a Ruined Baffle - a type of defect occurring in glass packaging

Ruined Baffle

Excess of glass (flash) appearing whitish in color (like crushed glass), situated on the baffle line.


Diagram showing Folds - a type of defect occurring in glass packaging

Folds

Almost horizontal concavities on the outer surface of the item; shallow, open wrinkles.
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Diagram showing a Washboard Marks - a type of defect occurring in glass packaging

Washboard Marks

Fine horizontal ripples on the glass surface.




Diagram showing Brush Marks - a type of defect occurring in glass packaging

Brush Marks

Numerous fine vertical marks, often on the shoulder.





Diagram showing Orange Peel Marks - a type of defect occurring in glass packaging

Orange Peel Marks

Rough, bumpy surface that resembles the texture of an orange.




Diagram showing Toad Skin Marks - a type of defect occurring in glass packaging

Toad Skin Marks

Glass is regularly distributed, but the exterior is not smooth (covered with small plates) and it is characterized by a grainy and dirty aspect, similar to the skin of a toad.​​​

Diagram showing Seeds - a type of defect occurring in glass packaging

Seeds

Very small gas bubbles in the glass mass, < 0.8 mm.






Diagram showing Fire Cracks - a type of defect occurring in glass packaging

Fire Cracks

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.

Diagram showing Chain Marks - a type of defect occurring in glass packaging

Chain Marks

Marks on the bottom of the bottle caused by contact with the conveyor belt immediately after manufacture.


Diagram showing a Crizzled Bottom - a type of defect occurring in glass packaging

Crizzled Bottom

Small axial grooves grouped around the baffle line.






Diagram showing a Cracked Bottom - a type of defect occurring in glass packaging

Cracked Bottom

Web-shaped cracks.






Diagram showing Bad Engravings - a type of defect occurring in glass packaging

Bad Engravings

The engravings on the glass are difficult to read to a greater or lesser extent.




Diagram showing Oil Marks - a type of defect occurring in glass packaging

Oil Marks

String of grey bubbles inside the glass.






Diagram showing a Neck Hollow Finish - a type of defect occurring in glass packaging

Neck Hallow Finish

Depression in the thickness of the glass in the finish or neck.





Diagram showing a Dirty Neck - a type of defect occurring in glass packaging

Dirty Neck

Black spots (grainy aspect).






Diagram showing a Bulged or Unfilled Finish - a type of defect occurring in glass packaging

Bulged or Unfilled Finish

Bulged out of shape finish, either by blowing or mechanical action. May prevent good capping of the container.


Diagram showing Folds Inside Finish - a type of defect occurring in glass packaging

Folds Inside Finish

Vertical marks inside the finish.






Diagram showing a Glass Trimming - a type of defect occurring in glass packaging

Glass Trimming

Protruding ridge of glass around the upper part of the finish (thin rim of glass) > 0.2mm.




Diagram showing a Seam Under Finish - a type of defect occurring in glass packaging

Seam Under Finish

A seam ≥ 0.5mm, situated on the joint between the finishing mould ring and the blank molds.



Diagram showing a High Finish Seam - a type of defect occurring in glass packaging

High Finish Seam

A seam of glass ≥ 0.2mm, on the joint between the two sections of the neck ring mould.



Diagram showing Folds On Finish - a type of defect occurring in glass packaging

Folds On Finish

Vertical or horizontal external marks on the finish, purely an aesthetic defect.



Diagram showing an Out of Round Finish - a type of defect occurring in glass packaging

Out of Round Finish

The finish is not round.






Diagram showing a Rolled In Finish - a type of defect occurring in glass packaging

Rolled In Finish

Entry slough or extra thickness of the glass inside the finish.




If you're struggling to match your particular defect or you're looking for further information, we're here to help so give us a call on 01355 236 170, email, or jump on the web chat function during our usual business hours and we'll be glad to assist.