With Halloween in the air, we need a scary posting. What is more scary than a bucket of sulfuric acid, a current generator, liberated highly flammable hydrogen gas, and blood-red dye? Heck, I took my life in my hands for this posting; just to make it more edgy, I even invited a knife thrower from the touring circus to come over and practice on me while anodizing some aluminum bench dogs for fun and definitely not for profit.
Thing is, Steve said "I can make them, but they won't be anodized like the regular ones". That got me thinking of anodizing them as a test.
I based my procedure on a great article written by Jim Bowes "Anodizing at Home". Mine will be a photo version of his document along with some observations and tips not present in the article. Overall, I had good success with some other aluminum dogs, but these from Qwas had been polished with an automotive protectant and I didn't know that first time around. That said, you'll see some pictures from the first round and second round intermingled. If a dog has a bit of color when you don't expect it, it is from round two; ignore it... nothing to see here :) Due to this protectant I wasn't able to 100% remove, a couple Qwas dogs were a bit lackluster.
- Sulfuric acid, commonly called battery acid; buy it at an automotive supplier in a 6 qt box for next to nothing (I got mine at Car Quest)
- Manual battery charger. I initially used an automatic battery charger (regrettably in some pictures); while great for charging a battery, it intelligently determines that the acid bath isn't really a battery and won't work correctly. The charger should supply 2A at 12V.
- Roll of aluminum foil; this is the sacrificial stuff.
- Roll of aluminum un-insulated wire; I found a long spool at Ace Hardware in the picture framing section.
- Rit Dye commonly available in the laundry section of a grocery store or in great variety at a crafts center.
- Aluminum angle (not shown). Get this at the Borg where the angle iron is. I got 1/2"x1/2". Cut into two lengths slightly longer than your baking dish (they sit on it). You will see them in use later; optional but highly recommended.
- Glass baking dish; (not shown) I used this for the acid bath.
- Oil drip pan; (not shown) this can hold the baking dish in case of splashes and makes a handy place to tape the leads.
Start, shall we?
First, googles or at least good eye protection, gloves, and clothes that won't hang into the acid bath are a must. The battery charger will put 2A through whatever is between the poles... whether that's the acid bath or, say, your heart if you touch the poles with each hand. The reaction liberates hydrogen so ventilate like you just ate the biggest burrito of your life. Pay attention. This is easy, but don't try for a Darwin award.
Okay, really start now...
The parts need to be clean. The dogs with a loop were 2-3 years old and raw. They just needed washing with soap and Simple Green. While I didn't initially know it, the Qwas dogs were polished on the lathe with an automotive protectant and wax. To clean these, I used 600 grit wet/dry paper then soaked them in acetone overnight. It wasn't completely cleaned, but I'm okay with it. While Jim's article recommends a nitric acid wash, I found it too difficult and/or expensive to get here. Acetone will dissolve nearly any finish or wax. A sanding with 600 or even 1200 grit wet/dry sand paper will not sand-down the part, but will polish the surface mechanically and remove a lot of grime. To me this is faster, easier, cheaper than mucking with nitric acid and hazmat fees.
Pour the dye mix into a sauce pot large enough to immerse your part. You want this at room temperature when you finally drop your anodization parts into the dye so if you just mixed it, set the pot in a shallow dish of cold water to cool it faster.
This picture shows my improved setup for the acid bath connections. The lengths of angle aluminum span the dish. The foil paddle has its wires come up and loop the aluminum and the cathode clamps over the wires to the bar for a very solid connection. Similarly, the anode clamps over the wire from the part. If you had a tall dish, you could easily suspend the part from this setup. This one is a winner.
While the anodization proceeds, get a plastic dish and fill it halfway with cold water.
What has happened to the parts so far is to build a thick surface of oxidation ("rust") on the surface of the parts. Unlike common ferrous rust, aluminum rust just looks a little pale and doesn't flake off. The oxidation layer is very porous so the dye will settle into the pores giving the color. We need to seal the surface to lock in the color. The rust collapses when subjected to heat like that found in boiling water. At this point, you could transfer the parts to a pot of boiling water for a few minutes to seal the surface. Thing is, some of the dye will leach off before the pores seal. What to do!
(cloth in this case). I brought it to a boil and left them there for 15 minutes.
- Black dye likely won't make specs like red did in my case; however it is important to note that the specs only happened on the Qwas dogs that had the protectant. This could be related.
- The second time I anodized, it took very little time getting to the point of waiting for the process to complete. While the parts boiled in dye, I put the rest away. Very fast process dispite the seemingly long instructions :)
- The un-anodized aluminum sanded easily; I tried sanding an anodized aluminum part and found it very hard by comparison. Besides beautifying the part, it makes them much more durable. If you didn't want the color, but wanted the strength, you could do all this with out the dye; just boil in water.