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lwalker
05-01-2008, 01:30 PM
I'm making a small part in aluminum and need to color it (actual color not that important). I figured I'd try anodizing since it looks fairly easy and I can probably use potassium permanganate to get a nice purple.

Believe it or not I can't find a source for battery acid short of buying a cheap battery and pouring it out! None of the car parts dealers I looked at carry the stuff and the only other source I can think of is industrial chemical suppliers and I know what they are like to deal with :-(

Any ideas? There's that Brownell's stuff, but it implies that it's really for touching up already anodized stuff.

davidh
05-01-2008, 01:32 PM
my local auto valu auto parts store has it in gallons, really reasonable. maybe even smaller containers but i needed the gallons.

you could also try a lawn and garden repair shop. their batterys most likely come without acid. . .

davidh
n.w. wisconsin

Mcgyver
05-01-2008, 01:36 PM
won't help you in Minn, but I walked into Elfstom Scientific and walked out with a bottle of 90% sulfuric acid, I diluted it down to battery acid levels as a pickle. They have a retail store but i think most business is supplying school boards etc - you might check out businesses selling science supplies

Evan
05-01-2008, 02:14 PM
Anybody that sells batteries should have H2SO4. They have to fill the batteries with something besides water. I did have to buy a 25 liter bag when I began doing anodizing. H2SO4 keeps well though.

DO NOT USE postassium permanganate anywhere near sulphuric acid. The two combine to make a powerful explosive, manganese oxide. It is a contact explosive which mean just touching it can set it off. Instead you can dye the aluminum with ordinary fabric dye. Potassium permanganate is a powerful oxidizer anyway and the item won't stay purple for long as the permanganate will react with everything that touches the article and leaves a trace, like fingerprints.

wschoenbeck
05-01-2008, 02:35 PM
Here in San Diego I found a drain cleaner product years ago at Home Depot that was 93% Sulfuric acid. I've had it out in the storage shed for quite a while. Although Evan says it keeps well I don't know if that means years. It is, I assume, industrial grade, very dark brown in color with an oily viscous appearance (oil of vitriol eh?).

I have not seen that product at HD since but I did run across it at another local lumber yard known as Dixieline lumber here in town recently. Unfortunately I don't recall the name. It was in a very non-descript 1/2 gal plastic jug that was in turn contained in a clear heavy gauge plastic bag.

Doesn't help other locations except to say look at the bottle and read the contents. It might show up in unlikely places.

hwingo
05-01-2008, 02:46 PM
I think you may have Fleet Farm at your location. I purchased a liter from Fleet Farm in Clintonville, WI. Also, NAPA sells H2SO4 in Wisconsin. Harley Davidson, Honda, etc are other possibilities. If you are at the location shown on your posting, there is no way a city that size would not have H2SO4.

Good Hunting,
Harold

Mark Hockett
05-01-2008, 03:33 PM
Most Napa auto parts stores carry battery acid.

lazlo
05-01-2008, 03:44 PM
Most Napa auto parts stores carry battery acid.

Battery acid is around 40% concentration of sulphuric acid.

The toilet bowl cleaner wschoenbeck mentioned at Home Depot and Lowes is over 90% concentration. I bought a bottle about a year ago, and it had a non-descript blue label.

lwalker
05-01-2008, 05:01 PM
Thanks. I can check there in person. I had searched their website but it's not there, and since most sites would normally say something like "In-store only item," I assumed that meant they didn't carry it at all.

Failing that, I am near a Fleet Farm. Guess I should update my profile: haven't lived in Minneapolis in years.


Most Napa auto parts stores carry battery acid.

KyMike
05-01-2008, 07:24 PM
Fabric dye works for anodizing, sort of, but it may not be permanent. I once anodized a cast aluminum part for a friend, using Rit Navy Blue dye. At first it looked good, but after the piece spent a few days on the dashboard of his truck in the sun, the purple color started to fade and a few weeks later was almost gone. For indoor use it would likely be ok, and it could be that something about the composition of the metal in the casting had an effect also, but I did read somewhere that dyes made for anodizing have additives to resist the effect of UV light.

Mike

Evan
05-01-2008, 07:52 PM
Nearly all dyes will fade in direct sun. To prevent fading pigment based colors are used. That is a problem for anodizing since the pores in the aluminum oxide are so small that many pigment particles won't fit.

Compounding the problem is that the parts need to be very thoroughly washed before dyeing. Any trace of acid left in the oxide coating will attack the dye molecules and bleach them.

You can of course buy professional anodizing dyes but they are expensive. I make sure the parts have a maximum depth oxide coat that gives maximum room for dye molecules. I also make sure the pre dye wash tank is kept slightly alkaline with the addition of small amounts of bicarbonate of soda. This ensures that no acid is "dragged" into the dye bath or trapped in the pores of the part.

Mark Hockett
05-01-2008, 09:00 PM
Battery acid is around 40% concentration of sulphuric acid.

The toilet bowl cleaner wschoenbeck mentioned at Home Depot and Lowes is over 90% concentration. I bought a bottle about a year ago, and it had a non-descript blue label.

It really doesn't matter what concentrate you use as long as you get the acid ratio correct in the anodizing tank. Battery acid is very easy to use for anodizing because you mix it 50/50 with distilled water and it gives you a good anodizing acid ratio. It can be a pain to get it right with other concentrations, I have to use a titration test in my commercial anodizing line to maintain the correct acid ratio.

JRouche
05-01-2008, 11:38 PM
I can buy sulfuric acid, along with other types, at my local pool supply store. Pretty cheap too in one gallon jugs. JR