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Troubleshooting Cyanide Zinc Processes


Alkaline cyanide based zinc plating processes (our Miromac range) have long been the "workhorse" of the zinc plating industry (although they are now less popular in the UK due to Health and Safety reasons). They are easy to operate and maintain and are relatively insensitive to the quality of the pretreatment of the substrate to be plated.


Select the problem from those listed below:

Lack of Overall Brightness

Dullness in LCD Areas

Dullness / Streaking in MCD Areas

Poor Deposit Thickness Distribution

Poor Plating Efficiency

Poor Adhesion / Blistering



Lack of Brightness

This problem is most usually caused by low brightener levels in the bath or an imbalance in the basic bath analysis (Zinc:Cyanide ratio or level of free sodium hydroxide). Try an addition of brightener to a Hull Cell test sample as recommended in the data sheet for the process that you are using. If this cures the problem, you can add an equivalent quantity to the process tank. If brightener does not cure the problem, check the bath analysis and correct as necessary. Make sure in particular that the zinc/cyanide ratio is correct for your process.

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Dullness in LCD Areas

This problem is due to either a lack of brightener in the bath, and imbalance in the zinc/cyanide/sodium hydroxide ratio or the presence of metallic impurities in the bath. Proceed as detailed in the "lack of brightness" section first. If this does not cure the problem, try an addition of "Doctor Solution" which will precipitate any metallic impurities from the bath as sulphides. To minimise the risk of metallic impurities, make sure you used good quality materials for process maintenance and good quality zinc anodes with low lead and cadmium.

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Dullness / Streaking in MCD Areas

This problem is caused by a buildup of brightener breakdown products and may occur in instances where the bath has been overdosed on a regular basis. In these cases, it is recommended to send a sample of the solution to the MacDermid Technical Centre for corrective analysis.

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Poor Thickness Distribution
This problem is usually caused by an imbalance in the zinc/cyanide/hydroxide ratio. It can be corrected by analysing the bath and re-balancing using the appropriate chemicals.

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Poor Plating Efficiency

This problem may have several causes. These are as follows:


Low Bath Temperature
Very High Carbonate (above 80 g/l)
Low Zinc Concentration
High Brightener Concentration
Bath Contamination


The temperature and zinc concentration can easily be checked and corrected. High carbonate can be a problem in solutions with low dragout. It can be removed by "freezing out", either using special equipment or pumping out the bath after winter shutdown.

High additive concentration can be a potential problem. It can happen if additions are not properly monitored or if dosing pumps become faulty. Bath contamination is quite common. Pretreatment is rarely perfect on commercial zinc plating lines and oil or other contaminants can be dragged into the bath.

If the carbonate is low, the zinc concentration correct, the bath temperature OK and plating efficiency still poor, the most likely cause is high brightener. This will usually plate out fairly quickly. If temporarily stopping brightener additions does not correct the poor efficiency, send a sample to the MacDermid Technical Centre.

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Poor Adhesion / Blistering

This is not common in cyanide containing processes, but can be caused by the following factors:

Poor Pretreatment (very greasy work)
Very High Brightener Concentration
Unsuitable substrate (for example leaded steel)


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