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anode shadow

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  • anode shadow

    I have been reading through the various post and came across the term “anode shadow”. Could someone explain this term and does it have an effect on dyed parts? Does the cathode have to have the same surface area as the part being anodized otherwise there may be some discoloring during the dying process?

  • #2
    I think you mean cathode shadow.

    This can occur when something else that is at anode potential (electrically connected to the anode) is placed between the anode (the work) and the cathode. When the distance from the shadowing piece is much closer to the work then is the cathode this can occur. The effect is a thinner anodic coating on the work in the "shadow" of the offending piece. This can be alleviated by repositioning the cathode or by use of multiple cathodes. Cathode shadow is rarely a problem when anodizing one suspended piece at a time, it can become a problem when using racking or anodizing multiple suspended pieces.

    If you are using a Constant Current (CC) power supply (highly recommended) anode vs. cathode area is not at all critical, CC adjusts automatically to accommodate the actual ratio. Generally, we recommend that the ratios be more or less equal, there is no harm if the anode : cathode ratio is 3 : 1, or as much as 1 : 100. This is not the case if Constant Voltage (CV) like a battery charger is used, here the ratio will effect the current density if it is not compensated by manually adjusting the voltage.


    • #3
      Thank you, I had read a line in topics that mentioned anode shadow and was wondering if this would be a problem I needed to pay attention to. I purchased the deluxe kit with the CC power supply. Before my purchase I read through some of the topics and discovered that the CC power supply would alleviate much of the guess work.

      I’m still setting the kit up and haven’t started the process of anodizing yet but hope to be up and running in a week or so. In the meantime if you could offer any other basic pointers or suggestions they would be most welcome to this novice. Thanks again


      • #4
        The best advise would to go slow and careful. Its not that anodizing is that hard, but it will be strange to an individual without any electrochemical backround.

        Do what you've been doing; read a much as you can find here and elsewhere, if you don't understand something ask. Don't just guess, or ignore an instruction, they are all there for a good reason. You should read all of the stickys at the top of this page carefully, there is also a reason that they are sticky.

        As always; the number one cause of anodization problems for beginners is the electrical connection to the work, this alone accounts for 90% of the problems. I'm speaking from long experience here.

        You don't need welded connections, unless you would rather avoid the inevitable connection issues entirely right at the start. All of us here bolted or threaded the connections with aluminum wire long before there was any Sputwelder. And we all learned to hate bolting and threading, but with enough effort we all made it work.