72 TA : New Project

[njsteve]

It does take time and you have to continually check on the progress so you dont get to the point where the anodizing is gone and your aluminum trim starts feeding the chemical reaction instead. Here is the trim after about 5 hours. You can see the tiny foaming bubbles rising from the trim pieces.



Here is what the piece looked like at the 8-hour mark. You can see most of the anodizing is gone except in the corner area, whcih was the slowest area to dissolve.

[njsteve]

After seeing what the Purple Stuff did I set up a plastic pipe capped at the bottom and filled with the Purple Stuff. I then hung the straight price of trim on a wire and hung it in the pipe.



Here it is after 30 minutes:



And after 2 hours:



You need to check this solution frequently and use a Scotch Brite pad or 0000 stainless steel wool to scrape the anodized crust off of the surface. This allows the chemical to get a better bite at the surface and continue the process. The Purple Stuff does work very well and very rapidly but seems to reach a point of diminishing returns after a few hours.

[njsteve]

The reason I used the Purple Stuff and tube method on the long piece was simply, that it was too long to fully submerge in the kiddy pool. You have to have the entire piece submerged otherwise you get uneven stripping and a big parting line in the trim piece.

Once the Purple Stuff did its work I then washed it in cold water and then transfered the straight trim piece to a section of plastic gutter lined with the same 6-ply plastic sheeting. I filled it with some of the same lye and water solution from the kiddy pool. You can see that the 2 chemical method (Purple Stuff followed by lye/water) works well as the lye solution immediately started taking away the remaining anodizing.

[njsteve]

From start to finish it took 12 hours of soaking in the lye solution to remove all of the anodizing. This included the periodic removal of the trim from the solution, the scrubbing of the surface and washing with cold water and then replacing in the solution again. I think if you used a higher concentration than one can per 10 gallons of cold water you would get faster results. One website I found suggested 1/2 cup per gallon of cold water. But since I was trying not to poison everyone in the house I decided to do the conservative method. When I was done, I poured the drain cleaner solution down the slowest sink drain in the house, which cleaned that up a bit as well. As for the trim pieces, I placed them in the shower and hosed them down with cold water for 5 minutes or so to get all the residue off.

One additional thing to remember. You must use proper protection: heavy rubber gloves and safety glasses are a minimum, plus proper ventilation.

Here is the before on the corner piece:



Here is the after:



And here are the other pieces, all ready for polishing this weekend.






This was a cautionary reminder I found on one website concerning using this method:

"Fast and easy, maybe. Dangerous, absolutely. Just one more reminder that every year trained professionals wearing protective gear are seriously injured when something goes wrong making up solutions of sodium hydroxide. It has an enormous "heat of solution" / "heat of dilution". This means when sodium hydroxide is mixed with water, it heats up the water. Not a big problem if a small amount is well mixed into a large amount of cold water. But if a small amount of water mixes with a large amount of sodium hydroxide (which can happen even in a large tank with poor mixing), that small amount of water is instantaneously turned into steam and erupts the contents of the tank all over the operator."

http://www.finishing.com/3600-3799/3674.shtml

[Verne_Frantz]

Steve,
Based on your last precautionary statement, I will add the "rule of thumb" for mixing caustics or acids with water. ALWAYS, add the caustic or acid to the water, never the reverse. IF the water is already there when the chemical is added, it will instantly be diluted and will not result in a violent reaction (erruption). Water first; chemical second.
Even when cleaning your home drains, never pour the chemical in a dry drain, then add water. ALWAYS run water first, then add the chemical.
Verne

[njsteve]

Wise precaution, Verne.

BTW, Here is a link to a site that has the % concentration of Sodium Hydroxide in various items. It's so nice to see that Crest Tooth Whitening Strips have the same ingredient of Sodium Hydroxide as Purple Stuff and Drano. Though the powdered Drano ranges from 30% to 60% Sodium Hydroxide and the purple stuff is only 1% to 5% concentration.

http://hpd.nlm.nih.gov/cgi-bin/house...chem&id=19

[Nova Jed]

I have read about this (sodium hydroxide) process before in a resto magazine, but do you know if the trim could be reanodized after it's stripped off? Or is it best to polish the trim and keep up with it? Any tips or info would be appreciated. Looks pretty good by the way!

[njsteve]

I believe this is basicaly the same process the commercial anodizers use. Here is a link to one of them and how they do it:

http://www.focuser.com/atm/anodize/anodize.html

[Nova Jed]

Thanks!

[ANDY M]

One thing that I still remember from High School Chemistry,
"Do as you outta, add acid to water".
The demo that the teacher gave was very convincing.