Glass products are used frequently in POS and promotional items. Therefore, if you’ve decided to use glass as a material for your next project, it is important to understand the process of glass manufacturing. Having a good understanding of what factors effect the quality during the manufacturing is essential. This ensures your product is made to the highest standard. When manufacturing promotional glass bottles 3 main materials are used. Silica Sand, Soda Ash and Limestone. To reduce the energy needed during production, cullet (recycled glass) is also added to the raw materials.

Maintaining quality during promotional glass bottle production

Manufacturing promotional glass bottles can be done using two methods Blow & Blow or Press & Blow. Both of these methods require stringent quality checks. This is to certify high quality products are manufactured. Moreover, it ensures any defected items do not enter the market. Two processes are used to check the quality of products. Firstly, items are check for defects. There are 3 categories of defects when manufacturing glass products namely, Major, Minor and Critical. Minor defects are generally aesthetic, whereas major and critical defects can be potential dangerous. Secondly, tolerances are checked. This ensures bottles are constant in height, shape and glass thickness.

Producing High Quality Glass Products - Promotional Glass Bottles Manufacturing Tolerances

Producing High Quality Glass Products – Promotional Glass Bottles Manufacturing Tolerances

Identifying  defects in production of Promotional Glass Bottles

Below are a list of Major and Critical defects that can occur during production of promotional glass bottles

Critical Defects

  1. Stuck Plug. A piece of glass, usually very sharp, projecting inwards just inside the neck bore.
  2. Overpress. Is a defect where a small ridge of glass has been formed on the sealing surface of the finish.
  3. Split. An open crack starting at the top of the finish and extending downward.
  4. Check. A small, shallow surface crack, usually at the bore of the container.
  5. Freaks. Odd shapes and conditions that render the container completely unusable. Bent or cocked necks are a common defect of this type.
  6. Poor Distribution. Thin shoulder, slug neck, choke neck, heavy bottom are terms used to describe the uneven distribution of glass.
  7. Soft Blister. A thin blister, usually found on or near the sealing surface. However, it can show up anywhere on the glass container.
  8. Choked Bore. Excess of glass has been distributed to the inside of the finish or opening.
  9. Cracks. Partial fractures, usually found in the heel area.
  10. Pinhole. Any opening causing leakage. It occurs most often in bottles with pointed corners.
  11. Filament. A hair-like string inside the bottle.
  12. Spike. Spikes are glass inside the bottle.
  13. Bird Swing.  Glass thread joining the two walls of the container.

Major Defects

  1. Chipped Finish. Pieces broken out of the top edge in the manufacturing process.
  2. Stone. Small inclusion of any non-glass material.
  3. Rocker Bottom. A sunken centre portion on in base of the container.
  4. Flanged Bottom. A rim of glass around the bottom at the parting line.
Producing High Quality Glass Products - Promotional Glass Container Manufacturing Tolerances

Producing High Quality Glass Products – Promotional Glass Container Manufacturing Tolerances

Tolerances during glass manufacture

Tolerances are the allowed differences between individual glass products. In order to ensure production is consistent tolerances are set during manufacturing. Glass tolerances can be applied to most products. However, if the glass product has to fit inside a container e.g. aftershave and perfume bottles then the tolerances may need to be reduced.

Producing High Quality Glass Products - Promotional Glass Bottle Manufacturing Tolerances

Producing High Quality Glass Products – Promotional Glass Bottles Manufacturing Tolerances

Reducing defects during manufacturing

Producing consistent glass bottles is easily achievable during mass production. However, from time to time defects can occur. Most of the time these defects are minor. Despite this, defects can sometimes cause minor size differences in bottles. Below are the two most common types of defects, how they are caused and what can they be done to prevent them.

1. Uneven or bad distribution of bottle body


Uneven wall thickness.


Feeder – Uneven glass temperature.

Machine Setup and Operation – Uneven cooling of blank moulds, Incorrect drum setting, Excessive blank cooling, Settle blow time too long, Counter blow time too short, Machine speed too low, Incorrect timing of gob delivery.

Mould Equipment – Blank design unsuitable, incorrect plunger design.


Adjust glass temperature, Apply cooling air evenly on the blank moulds, Adjust drum setting, Adjust blank cooling, Reduce settle blow, Increase counter blow time, Increase machine speed, Check loading position, Adjust blank design, Adjust plunger design.

2. Out of shape ware


Container tilted to one side due to bottom not being level.


Feeder – Glass too hot.

Machine Setup and Operation – Insufficient final blow time and/or pressure, Incorrect application of cooling wind – mould too hot, Machine speed too high, Blow mould cycle too short, Unsuitable ware pusher design, Container not hanging in the takeout long enough.

Mould Equipment – Change the blow mould, Correct Blank design.

Conveyor – Incorrect cooling over the dead plate, Pushout moving bottle onto the conveyor too soon.


Adjust feeder temperature, Increase final blow time and/or pressure, Adjust mould cooling wind, Adjust machine speed, Increase blow mould cycle, Improve ware pushers design, Reduce time in takeout position, Increase run time, Change the blow mould, Correct blank design, Adjust cooling over the dead plate, Delay bottle moving onto the conveyor, Check movement of container on the conveyor.

Producing High Quality Glass Products - Promotional Drinks Glass Manufacturing Tolerances

Producing High Quality Glass Products – Promotional Glass Bottles Manufacturing Tolerances

Quality Control during manufacturing

Quality control reduces defects in production. Following the steps below results in the reduction of errors.

  • Test bottles at regular intervals during production.
  • If any bottle in the round fails testing, four additional bottles need testing.
  • If a failure occurs among the four bottles tested then all bottles should be rejected until fault has been rectified.
  • When all four bottles pass testing production can continue.
  • After initial failure has been verified, all pallets loaded with bottles produced from the last unsatisfactory test are detained.
  • Once nonconforming bottles are removed detained pallets are released.

Need help producing high quality glass bottles? Get in touch.

Custom glass products require expert knowledge to ensure a high quality product. ODM are experts in designing and manufacturing high quality, promotional glass products. If you need assistance with your next project contact us. Our team have experience in designing and manufacturing high quality promotional products.

Want to know more about promotional glass products? Check out this case study.

Check out this unique whiskey glass. Perfect for a drinks promotion.

These lightbulb glasses are a fun and unique promotional idea.