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#03 Bacterial degradation of semi-finished products: what to do?

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In ceramic, semi-finished products are all those materials (in our case, aqueous suspensions) that are produced beside the main production line and that are used in several phases of the process, mostly along the glazing line.


We can include in this category, for example:


  1. Grinded glazes
  2. Engobes
  3. Grit suspensions
  4. Liquid suspension of oxides and dyers


After they have been managed and prepared for the final application, aqueous suspensions usually rest inside the storage tanks for shorter or longer times, waiting to be used.


1. Water & Organic Matter: the roots of the problem

It is exactly during storage that the problem may occur. The simultneous presence of WATER and ORGANIC MATTER (a nourishment for bacteria), in fact, is the basis of possible degradation phenomena.


Bacteria usually start their work when water is added within the tanks.
This is the reason why bacteria degradations are usually unusual within powders or product that do not contain water.
Bacteria use the organic matter of the suspension as a source of food, activating their metabolism and therefore their contaminating activity.


What are the main ingredients that can be easily attacked by bacteria?


  1. INORGANIC RAW MATERIALS (such as pigments, clays, feldspar, and nepheline)
  3. NATURAL OR SYNTHETIC CHEMICALS (that can be both organic or inorganic and that be used according to the needs)


2. Where do bacteria come from?

Once we have defined what is the mix that may cause a possible contamination, it is important to examine where bacteria come from. Which is their origin?



In general, bacteria are almost always present in raw materials of natural origin (such as sands, feldspar, and clays). They can also widely be in the grinding waters as well as in the atmosphere. Bacteria can finally be found within the containers and/or on all those tools involved in the semi- finished products preparation. 

It is also important to point out that bacteria activity is affected by the season or, even better, by the temperature. This means that during the hotter and wetter periods bacteria’s metabolism is exponentially faster, therefore causing generally more attacks.


3. Consequences of a bacterial attack 

What happens within the suspension when it is under attack?

Bacteria, as we already underlined, “eat" the organic matter and so also the organic parts of some chemicals that play an important role in providing the suspension with the proper rheological parameters (that are required for a perfect application process), suche as viscosity, proper flow limit, absence of sedimentation phenomena, etc. Bacterial degradations, since they partially or totally undermine the suspension’s rheological features, totally compromise the application phase.


On the top of that, METABOLITES give their contribution to make the situation worse.
Metabolites substances are all those substances produced by bacteria: they are basically the waste of their nutrition and they are responsible, together with other elements, for different kind of defects.
In application: improper suspension’s leveling, sedimentation and/or foaming phenomena, bad odors, etc
During the firing cycle: pins in the glaze, etc.


4. Actions & Solutions

How to manage the problem?
Is it possible to restore the original features of a compromised suspension?


We can surely say that it is possible to take effective actions when degradations are not particularly aggressive. That is when number of bacteria and of organic waste is not to very high. Once we have understood how serious the problem is, and therefore we have understood what we must do, a two-step approach is recommended: 


  1. 1. Eliminate and so kill the bacteria by using proper biocides and preservatives agents
  2. 2. After a careful analysis within the labs, restore the suspension’s rheological features by using the proper chemicals


5. Environment & Time Variable

Once the suspension has been restored, it would be important to make a thorough analysis of the working areas. The check should be done not only where semi-finished products are prepared but also in all that areas where they are applied. This is very important to test the presence of bacterial colonies in the atmosphere that could affect the products that are placed in the industrial plant.

It is obvious, but it is also important to underline that this kind of control is recommended also without bacterial attack in order to take actions useful to prevent a possible aggression.



Even the time variable is very important.The efficiency of preservatives agent progressively runs out, in fact, as they work against bacteria: we could say in some ways that preservatives “die” together with bacteria. In the same way, the additives’ efficiency can naturally finish over time. For these reasons it is important to restore (or add over time) the medium inside the suspension to assure an efficient and ongoing action.


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