Uneven results from dimmer switch anodizer

Here’s another question I frequently get:

I followed your instructions on building an anodizer and I would like to say that you have made a great job illustrating it. My anodizer is the dimmer and light bulb type it delivers a maximum of 160 Volts.I prepared a solution of TSP in distilled water placed the cathode (aluminum foil) and the Ti at the anode ran the circuit. The voltage keeps rising slowly and I get shades instead of definite colors (mostly violet, golden and pale blue). I can’t hold the voltage at a definite value. What should I do to get smooth colors? I tried adjusting the voltage first then immersing the piece but the voltage after immersing is lower than what I’ve just set it to. Please help me out here and thanks in advance.
David S.

First of all, the dimmer based voltage control is going to be a bit temperamental and unstable. But I used one myself for years before replacing the dimmer with a Variac.

Aluminum should work for a cathode, but should be lightly sanded to remove the invisible insulating oxide layer that spontaneously forms. I usually use titanium, but have been told by many that stainless steel works well.

When you have a large capacitor smoothing a the choppy dimmer voltage, the top end will be a bit mushy. The lower voltages are the worst for this effect. The tan, violet and blues are at the low end of the voltage scale.

Another issue in getting smooth colors is getting the voltage everywhere simultaneously. You should have the piece to be anodized immersed in the solution before completing the circuit to the leads. That is, you need a switch to turn the leads on and off, while the anodizer is running at the voltage you want.

Cleaning and chemically etching the metal before anodizing also helps assure a uniform color, and is generally considered necessary for getting the higher voltage colors.

The voltage measured on the leads or capacitor will drop when you start anodizing, and should rise back to your preset voltage in a minute or so. The time depends on how big a piece you are anodizing, how big your cathode is, and on the efficiency of your electrolyte.

Another possible problem might be the material of your attachment to the anode piece. Only titanium or niobium should touch the electrolyte at the positive side. Never use copper wire or regular (galvanized or tinned) alligator clips to immerse your piece. The current will just go though that, and little will be applied to your piece.

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2 Responses to Uneven results from dimmer switch anodizer

  1. David S. says:

    I’d like to thank you for your effort. I’ve figured it out and I’m now getting even colors. What I did was that I replaced the lamps; the dimmer stabilizer with a 200 Watt instead of 100 and the capacitor drain with a 40 Watt instead of 60. This gave me an out put of 280 Volts max. As for the connection what I did was that I placed the Ti piece in the solution and then raised the voltage to maximum out put before closing the circuit. Later when I connect the circuit the voltage keeps rising and the color keeps changing evenly. Once the desired color is reached I open the circuit. I’ve also made some notes on the colors vs voltage and they are quiet different than Mr.Titanium’s. For example:
    Pale blue—>60v
    Yellowish green—>80v
    Yellow—>95
    Deep reddish violet—>126v
    Blue/Teal—>150v
    Teal—>157
    Thanks again

  2. MrTitanium says:

    Your voltage readings are very high for the colors specified. I usually get:
    Dark Blue->25v
    Pale blue—>40v
    Yellow—>55-65 (depending on surface finish and time)
    Deep reddish violet—>80-90v (depending …)
    Green—>95-110v (depending …)

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