On Sun, 22 May 2005 12:12:24 GMT, "Karl Townsend"
remove .NOT to reply wrote:

I made an aluminum knob to replace a plastic knob I didn't like on a
machine I otherwise like a lot. Then I black anodized it.

Hey Don,

Please discuss that anodizing a bit. Does it have a hard surface like the
commercial Job? Is this an easy to do thing like nickel chrome, or really
involved like triple chrome?

Disclaimer: I'm no expert on anodizing.

My understanding is that "hard" anodize has smaller pores that don't
accept dye as well. The process is the same, and it's easy to do; I
think the difference is that "hard" anodizing is done with more
concentrated acid at higher current and lower temperature.

The electrolyte is just battery acid from NAPA, diluted 2:1 with
distilled water for hard anodizing or 3:1 for a film that is to be
dyed. I do it at room temperature. Cooling the electrolyte might
result in a harder film. I really don't know how hard the film I get
is. I used a current of about 0.1 amp per square inch. I've read
that lower current will result in better dye saturation but I haven't
tried that yet. My knob isn't really a deep black, more of a
gunmetal color. A matte finish (beadblasted) might also result in a
darker black.

My "secret weapon" is using Ted Edwards' electrocleaning soup to get
the aluminum waterbreak clean. It's in the dropbox somewhere. I
don't use any electricity for that, just dip the work in the soup for
a few seconds and scrub it with a rag. It really does the job!

After anodizing, the work is typically sealed by immersing it in
boiling distilled water, perhaps with a sealant chemical added.

There are some good websites about anodizing, though I don't have the
URL's at hand. Google on anodize and telescope.

Caswell's plating manual has a good section on anodizing, and he sells
the dyes and some other chemicals like de-oxidizer and sealant.