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Reddish-brown opaque color in anodizing tank

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  • Reddish-brown opaque color in anodizing tank

    About a year ago I set up a small anodizing line according to the Caswells LCD guidelines. There's been a little bit of a learning curve, though for the most part things have been going smoothly. Just recently I went to run a batch and noticed the anodizing tank had taken on a reddish brown opaque hue. Until yesterday the tank had always been a translucent green/blue with a small amount of brownish material that would build up on the lead cathodes. Initially I thought it might just be from agitation, but a day later it still looks more or less the same. I might see if it settles out given more time.

    Some details on the setup -

    All tanks set up to the Caswells LCD spec
    Almost exclusively anodizing 6061
    Lead Cathodes, left in tank
    Titanium Racking
    Titanium aquarium chiller, little giant pump, all plastic fittings
    Parts mostly tumbled with Agsco JC 212 R degreaser then degreased in SP degreaser tank

    My understanding is that the color change could indicate copper contamination. But I thought that would be more of an issue with 2xxx and 7xxx alloys. And we've been pretty careful to keep copper and other metals away from the tank.

    Any ideas what could have caused the change? Is it even an issue?

    Cheers and thanks!

    Click image for larger version

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