OCT 20, 2017

Common Glass Defects

We’re a leading supplier of Magflux® blast furnace slag here at Blastrite, and firmly believe this is the ideal fining agent to use in the production of container glass. Used correctly, this can help to reduce the common causes of defects in glass, some of which we have listed here.

Inclusions Inside Glass

The term inclusion is used to describe any foreign object trapped within the glass during the manufacturing process. Inclusions might include hard items such as little grains, commonly referred to as rocks, or other imperfections such as glass bubbles, for example. Let’s take a closer look at each of these items in question.

Rocks: Manufacturers in the glass industry define rocks as hard grainy items that have become trapped inside the glass. Typically, these are tiny fragments of materials used inside the furnace which hasn’t burnt properly whilst the glass was being made. If they are not removed they can create issues in the glass including cracking of finished items.

Seeds: If you can see a tiny air bubble trapped inside a glass object this is referred to as a seed. This is caused when gas is trapped inside the glass when it is being made, during its molten state. It’s quite common to see glass objects with seeds trapped inside them and the odd few is nothing to be concerned about. However, if there are large numbers of seeds within the glass it can often be more difficult to work with, especially if you are working with glass sheets.  


When we refer to cords we are talking about large streaks of glass with a different composition to the rest of the material. Cords are often caused when areas of glass haven’t baked properly giving them a different property to the rest of the glass. Quite often, they are easy to spot within glass sheets because they look so different.

Physical Defects

Sometimes, it’s a physical defect that spoils the appearance of glass containers. These can include general finish defects on the neck, shoulder, body or base of a bottle. In many of these instances, the problems arise during the feeder or machine operation processes. By helping production staff to recognise the common defects, and by teaching them how to remedy these issues, you can produce good quality products.   

These are just some of the defects that sometimes occur during the production of glass items. Use quality blast furnace slag to reduce the chances of imperfections in container glass, and contact us here at Blastrite for more details or to place an order on +27 21 417 1700

Created on 20th October 2017
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