Dabney was sitting at his workbench when the Doctor came by the garage one morning. He was in the mood for a cup of Dabney's French Roast coffee and walked in expecting to smell fresh brew, only to find nothing on the stove.
"What's up," asked the Doctor, "How come there's no coffee?"
"Well, Doc," said Dabney, "I was going to make some while trying to polish this aluminum dash trim but I got involved rubbing away and forgot to do it. I'll get some coffee going now, since I'm not getting anywhere with this trim."
Dabney ground the beans and started the water boiling and then set up the filter and drip flask for the fresh brew. He occupied himself while the Doctor looked over the apparatus on the workbench. There were soft rags, aluminum polish, fine steel wool, cleaning fluid, paper towels and several waxes all lined up next to the work. The piece itself was a machine-turned piece of aluminum that was used as a dash trim on his old 1927 Bentley.
"Well, it looks like you've got enough material to polish a whole car here," commented the Doctor.
"I do, but no matter what I use to polish the old trim piece it just gets shinier without cleaning out the imbedded dirt and stains," said Dabney.
"That's because the aluminum trim is anodized, dear Boy," said the Doctor.
"So what?" said Dabney, it ought to polish up, ought'n it?
"If you scrub long enough it might," replied the Doctor, "but anodizing layers are very tough and it will take a lot of work to remove it before the aluminum surface can be cleaned and polished. Also, you'll get splotchy results."
"So how do you clean this up?" asked Dabney, "do I have to get a replacement made?"
"No," said the Doctor calmly, "all you need to do is de-anodize it."
"Huh?" said Dabney. "Don't I have to take it to a chrome shop for that?"
"Not at all," said the Doctor. "Let me explain a little about anodizing."
Dabney knew he was about to get another one of the Doctor's lectures, so he poured himself an extra large cup of coffee and the two of them sat down on the garage couch.
"Anodizing is an old, tried-and-true method of making the surface of aluminum (and other metals) much harder," said the Doctor. "In the process, aluminum oxide is grown out of the surface, becoming aluminum hydrate - an extremely hard material. The porous nature of the new surface allows it to be dyed any color desired, hence the frequently-seen colors of anodized aluminum in such things as hydraulic lines, bicycle parts, etc. Anyway, the basic steps in anodizing aluminum are: cleaning; etching; desmutting and anodizing."
The Doctor continued, saying, "The part is cleaned thoroughly and then etched in a caustic solution, usually lye, for just a few seconds to a minute. This leaves a layer of oxide, dirt and other impurities called 'smut,' that has to be removed by either wiping off or rinsing. Then the part is dyed and anodized by passing an electric current through an acid bath in which the part is immersed. The part itself is the anode in the electrical process. Once anodized, the surface is rendered very hard and durable."
"So that's why I can't polish it out, right?" said Dabney.
"That's right," said the Doctor, "so to be able to polish the aluminum surface properly you need to de-anodize it."
"Yeah, I know," said Dabney in a state of mild irritation, "so how do I do it?
"It's easy," said the Doctor, "all you need to do is immerse the piece in the same caustic solution that it was etched with in the first place: lye."
"Where can I get some?" asked Dabney.
"Chances are you have it right here, old Boy," replied the Doctor. "Do you have some drain cleaner around?"
"I have a can of Drano crystals over at the sink," replied Dabney.
"Read the label," said the Doctor.
Dabney did so, saying, "it contains sodium hydroxide."
The Doctor smiled, saying, "that's another phrase meaning lye, dear Boy."
Dabney ran some warm water into the basin and poured in some of the Drano crystals. He then put on rubber gloves and protective glasses and mixed the solution thoroughly. The trim piece was dipped into the solution for a minute or two, during which time some smut formed. This was wiped away and the piece was dipped again until the surface looked consistent. The smut was wiped away and Dabney was able to polish it to a brilliant sheen shortly afterward.