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!
A projection of glass extending upwards from the bottom on the inside of the jar or bottle.
A thin strand of glass across the inside of a container either between the walls or between the wall and the bottom.
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.
A fragment of glass of any size, attached or loose, inside the container.
Air bubbles trapped inside the glass mass to be found on the internal surface.
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.
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).
Sharp edges along the lines of the mould seams.
A fracture which usually occurs in the body of the article. It doesn’t always cause breakage.
Discontinuous surface cracks with one or more shiny parts (straighter crack: no protruding glass can be felt).
Foreign body in the glass.
When the finishing mold closes it blocks the structure and produces a heavy seam.
The finish is not completely regular; the thread profile has not been formed properly. There is glass missing from the top surface.
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.
Impact point from a knock that extends into the glass mass in a cone shape.
Internal marks of any kind (water, dust, cardboard, grease etc.) which cannot be removed by the preliminary washing procedure.
Any missing or incorrect engravings meaning that it is not possible to sell the article (capacity indication, spelling mistakes, etc.).
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).
Excessive treatment causes slippery bottles, no treatment causes friction on contact between containers.
Excess of glass in the neck which partially or completely obstructs the bore and doesn’t allow the filling tube to be introduced.
Depression in the thickness of the glass in the neck of a bottle.
The thickness of the glass does not meet the specifications.
The vertical axis of the neck is at an angle to the vertical axis of the body.
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.
The marks do not conform to the drawing or are missing.
Unwanted pieces of glass, which may or may not be sharp, stuck to the external surface of the item.
Usually elongated, they may be: Cracked (the outer surface is broken) or Not Cracked (but with a thin skin).
A small fragment of glass has been chipped off the finish (scratched), sometimes not completely detached.
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.
On the glass mass with radial crizzles, or on the external surface of the glass mass without crizzles.
Small glass protuberance on top surface of the finish, only in one point of the finish. <0.3mm not significant, ≥ 0.3 mm: defective.
When the offset is up to or more than 0.3 mm.
Beginning of a crack that does not pass through the entire thickness of the glass (usually in a straight line).
Slough or deformation of glass in the punt, making the bottle below capacity.
Imprint on the bottom due to poor fit between the baffle plate and the blank mold.
The article is misshapen, or the circumference is imperfectly round.
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.).
The finish axis is not aligned with the body, even though the finish and body axes are parallel and vertical.
Protuberance on the inside of the finish which can affect the finish during uncorking; no risk of scratching.
A markedly thinner area in the thickness of the glass which may cause fragility in the bottle.
Round protuberance inside the neck, not fragile.
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.
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.
Superficial and external mark with two separated, irregular rims. It can be situated on the bottom, and is normally not visible.
A mark on the surface of the bottle caused by the shears.
A surface crack under the finish, at the join between the finish mould and the preparatory mould.
The whole body of the article has shifted at one side by ≥ 1mm, the bottom axis is not aligned with the body axis.
The bottom is not completely perpendicular to the axis of the bottle. It may be inclined to one side or wavy.
The center of the bottom is lower than the external rim of the bottom.
The vertical axis of the finish is at an angle to the vertical axis of body.
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.
Irregular external surface. The body looks rough and wavy, with fine undulations.
An open mark/crack on the glass surface.
A thread of a different type of glass in the mass (a thin glass ripple that can be seen through the glass).
A thin ridge of glass along the parting line, caused by the mould joint.
Excess of glass (flash) appearing whitish in color (like crushed glass), situated on the baffle line.
Almost horizontal concavities on the outer surface of the item; shallow, open wrinkles.
Fine horizontal ripples on the glass surface.
Numerous fine vertical marks, often on the shoulder.
Rough, bumpy surface that resembles the texture of an orange.
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.
Very small gas bubbles in the glass mass, < 0.8 mm.
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.
Marks on the bottom of the bottle caused by contact with the conveyor belt immediately after manufacture.
Small axial grooves grouped around the baffle line.
The engravings on the glass are difficult to read to a greater or lesser extent.
String of grey bubbles inside the glass.
Depression in the thickness of the glass in the finish or neck.
Black spots (grainy aspect).
Bulged out of shape finish, either by blowing or mechanical action. May prevent good capping of the container.
Vertical marks inside the finish.
Protruding ridge of glass around the upper part of the finish (thin rim of glass) > 0.2mm.
A seam ≥ 0.5mm, situated on the joint between the finishing mould ring and the blank molds.
A seam of glass ≥ 0.2mm, on the joint between the two sections of the neck ring mould.
Vertical or horizontal external marks on the finish, purely an aesthetic defect.
The finish is not round.
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.