Can't get part to anodize!

A. Hi Ike. Chris' posting was from 22 years ago and his e-mail is bouncing. Again is there more bubbling on the part or on the anode? Our first guess is always that you have the polarity reversed, especially if you think bubbling on the parts is a good thing :-)

Luck & Regards,

A. Hi Ike.
If I were you I would switch to sulfuric acid right away. I have never heard of any kind of anodizing with vinegar, and although that certainly doesn't mean it can't work, trying such variations would be something for an accomplished anodizer to try to develop. When starting out, probably with no experience and no instrumentation, you're pretty much limited to following the cookbook :-)

Luck & Regards,

A. I don't have that book so I don't know whether you are following the instructions correctly, nor whether they are right or wrong. But the work must be the anode, and reading between the lines I still feel it's probable you have the polarity reversed.

The most obvious bubbles are hydrogen at the cathode. If there are also bubbles at the other pole, they are oxygen bubbles at the anode. Water is H20 so you will always have at least twice as much hydrogen as oxygen.

If the bubbling on your workpiece exceeds the bubbling on the other pole, and if the bubbling is fairly well distributed, it's probably hydrogen and the polarity is reversed. If there is more gassing at the other pole than on your work the polarity is correct, but....

Organic contamination will lead to release of oxygen at the anode; it's possible the parts aren't really clean.

I don't know if you are applying enough voltage, nor whether your acid is strong enough to attack the aluminum and create the porosity necessary for dye absorption. What kind of amperage and voltage readings are you getting and what is the surface area of your part?

Q. Hi, Thanks for the previous help but one last question. I've got the book Artists Anodizing Aluminum: the Sulfuric Acid Process [affil link on Amazon] and all my parts anodize great now. My question is how do I achieve a Gloss or semi-gloss finish after sealing. The parts look great as far as color goes but always have a matte finish. Do I need to clear lacquer everything? Thanx Chris

A. Hello again, Chris. Please tell the curious readers what changed that took you from no anodizing to satisfactory anodizing.

You do not need to lacquer your parts, but they will be no shinier, and actually a little less shiny, after anodizing them than before. If you want a bright finish you must polish/buff the parts before you anodize them. Good luck.

Regards,

A. Hi Richard.

- Don't start at 15 volts; you'll burn the parts before you've even started.
- Your 1.5 A is low by a factor of about 2. Figure 12 amps per square foot.
- Most heat sinks are anodized and thus not conductive.

Regards,

Q. The heat sink might have been clear anodized, I let it sit in Sodium Hydroxide till it was bubbling well. I don't actually "start" at 15v. I set the supply to 1.5A (although I hear varying amounts for ASF, a lot of 720 calculators say 6 ASF). But the supply is set to be locked at 1.5A (maybe should be 3A) and when I hook up the part, the voltage (which is floating) starts at 4.8v then by the time an hour is up goes down to 1.0v.

Should I put a power resistor into the circuit to increase the resistance in work circuit to get the circuit Voltage up to 12-15v? I figure (at 1.5A or 6 ASF) my resistance is around 3.5 ohms (if I'm reading 4.8v at start). So to get the system voltage up to 15v I'd have to add 6.5 ohms more.
does this make sense?

A. Hi. External resistors should not be necessary, and seem to add a complication. It may simply be that your power supply is defective, as there should be no reason for the voltage to decrease over time; it should be rising, not dropping.

When you start, the resistance is very low. That's why the voltage must be limited (which you are indirectly doing by limiting the current). As the anodized film builds, the resistance increases, and the voltage should be automatically increasing to try to maintain constant current.

Regards,

A. Hi Michael. It's obviously difficult to say what someone has done wrong on their first attempt in a multiple-step process, based simply on it not having worked. But I'd say that the wire material might be the first issue to address; see if you can get some 2024.

Regards,

Hi Michael,

Ted may be right, but 6061 sounds a reasonable racking material to me.

Check that your connection from rack to work is good and firm. If there is a momentary loss of contact, the point of contact on the rack will become anodised and will not continue to conduct current when mechanical contact is remade.

Harry

A. Hi cousin Zunnurain. Our "Introduction to Anodizing of Aluminum" should give you a good starting point if you lack experience in this. After reviewing it you may wish to ask some detailed questions. Still, you probably should start your practice on scrap stock rather than on an item that is important to you.

Please understand that if someone says they want to build an airliner or perform an appendectomy, the first thing we would need to say is "what is your starting point ... what do you already know?". Although anodizing a bucket is easier and less risky than those things, there is still a fair amount to it, and it still requires a starting point: the book "The Surface Treatment and Finishing of Aluminum and Its Alloys", for example, will answer all your questions but it's 1,273 pages :-)

Best of luck.

Regards,