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Foam layer growing on Anodizing & Electrocolouring baths

Quickstart:
     In the anodizing of aluminum the components are immersed into a tank of acidic solution and connected to the anodic (+) positive pole of a power supply. The current separates some of the water in the solution into positively charged hydrogen and negatively charged oxygen. The oxygen is attracted to the positively charged components and converts the skin of the aluminum to aluminum oxides.
     Readers new to anodizing of aluminum may wish to view our "Intro to Aluminum Anodizing".

I am Masood khan production supervisor working for Anodizing plant in Riyadh K.S.A.

we notice a foam layer in anodizing & colouring bath when the bath is not in use for 8 hrs.when we process material in colouring some inner surface is not coloured due to this foam entrapment.

This type of foam was not seen any time in past eight years.

Masood khan
Employee - Riyadh, Saudi Arabia.
July 17, 2008

A. Hi,

Am I correct in assuming that you use air agitation ⇦ huh? on the anodizing bath and that when it is in use there is no excessive foaming?
I suggest that you look in three areas.
1) Are you using a cleaner and that foam from this is being carried down the line on the racks?
2) Are you using an alkaline etch and using surfactants to suppress spray/mist? Or maybe oils and greases on the aluminium are being emulsified or saponified (made into soaps). Again foam from any of these causes could be carried into the anodizer.
3) Have you started to use a spray/mist suppressant on the anodizing bath? This can result in debris on the sides on the tank being clean off and causing "scum" on the surface of the tank.
Actions on (1) and (2) may need higher level of water in the rinses or the use of water sprays.
The stable foam on the anodizing bath will tend to act as a floatation medium for oil, grease and other soiling. It is likely that it is this suspended matter that coats the anodic film during transfer to the coloring tank and causes your problem.
If you cannot identify and prevent the cause of the foam, then you are left to skim it off from the surface of the bath.

Harry Parkes
- Birmingham, UK

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Foaming has been observed in both the anodizing and dye baths. The amount of foam increases significantly during the anodizing process, reaching nearly two to three times the level observed when the process is not in operation.

What could be the possible causes of this issue? What solutions would you recommend to address this problem?

(For reference, an alkaline degreasing step is included in our process.)

Ziak Ziakimbo
Engineer - Istanbul
March 9, 2026

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