This tutorial will show how I anodize aluminum. I learned this process studying art in college, and then set up my own anodizing tank with the help of the internet, and changed some things to suit my studio and the way I work.
Anodizing involves electricity and caustic chemicals. Work in a well ventilated area. Keep all chemicals labeled and keep everything involved in this process out of the reach of children. Do not attempt this process if you lack common sense.
Anodizing is a process of thickening the natural oxide layer that forms on the surface of aluminum. The obvious benefit of anodizing is you can add color to aluminum. Another benefit is it increases the wear resistance. Parts can be anodized and not dyed if you only want the wear resistance without the color.
There are a lot of alloys and many of them respond to anodizing differently. I typically use 6061 aluminum, it is a general purpose alu. and anodizes well. I have also used 1100, which is pure, or nearly pure aluminum. It anodized well, but was a miserable metal to work with because it was so soft. I have used other alloys but I don't know what they were. Some alloys do not anodize very well so I try to stick with the alloys I know work.
Titanium and some other metals can also be anodized, but that is a different process than the one I will be describing here.
Some of the colors I can anodize. Some of these I have made by mixing dyes.
Equipment needed and where it can be found:
power supply - I use a rectifier. This is the most expensive part of anodizing. I have heard anodizing can be done using a car battery charger, but I have not tried this, so I am not sure what exactly the requirements are for the charger. There is info about this elsewhere online. I already had a rectifier I used for plating, so I used it.
distilled water - Everytime I say to mix something with water, or to rinse the part or whatever, I am talking about using distilled water.
sulfuric acid - This can be found at hardware stores as a drain cleaner.
mix about 10-20% acid with distilled water. Always add acid to water.
This is what I am currently using:
aluminum rod - the positive wire from the rectifier will be connected to this. parts will be attached to this rod when they are anodized.
aluminum wire- to suspend the part in the bath. I use either 14ga or 18ga, depending on the size of the part.
electrical wire - positive and negative
lead cathode - I have read about the amount of surface area of lead you need for the size of the parts you will anodize... I don't worry about any of that. I am using 2 pieces of 1/8" thick 4" wide lead that hang to the bottom of the bucket.
dye - I use anodizing dye from caswell plating. The concentrated dye that makes 2 gallons costs about $8. The dye they sell must be heated to work properly. I use a crock pot, but it doesn't really matter how you heat it as long as it is heated. I have heard of people using Rit dye with mixed results. I have never tried it.
containers with lids for the chemicals - You definitely need lids for the sulfuric acid and caustic soda.
Caustic soda/lye/sodium hydroxide - Different names for the same thing. About the only time I use this anymore is to remove anodizing. This can be found as drain opener, it's usually sold in a granular form. Some of them contain something in addition to the sodium hydroxide. Try to find one that does not contain anything in addition to the sodium hydroxide. I bought some once that was white and blue granules, it didn't work so well. I was told that only the white granules are sodium hydroxide.
Some people also use the sodium hydroxide to etch the aluminum a little to clean it before anodizing. If this is done, most alloys need a second cleaner to remove the residue left on the alu from etching. Nitric acid, I think. I no longer do this step as it is not necessary if you clean the piece well enough.
I listed the suppliers I use at the bottom of the post.
Setting up equipment, mixing chemicals, purpose of various items:
I use 5 gallon buckets for everything. You can also use smaller containers, just make sure the part can be completely submerged without touching the cathode or sides of the container.
Its nice to arrange the containers close together and in the order they will be used. You dont want to have to walk across the room to rinse the piece then walk back to dye it. If the water starts to dry on the piece it can make the piece dye unevenly.
I wrapped one end of the lead sheet (the cathode) around a piece of brass rod and solderd them together. The rod is just so I have a way to hang the lead in the acid. Other anodizing tanks I have seen use aluminum for those kinds of fixtures, but I didn't have any at the time and I wanted to get things up and running. I have two of these sheets of lead hanging in the bucket. They are connected with a wire. Most other tanks I have seen use a cathode on both sides of the tank, so I did it too. The negative wire from the rectifier will attach to the cathode. Mine is soldered to the brass rod.
The positive wire from the rectifier is attached to a piece of aluminum (the anode). The parts are attached to this piece of aluminum.
I have cut slots on the sulfuric acid bucket for the brass rod and aluminum piece so they cannot move around in the bucket and so I can put the lid on.
I don't know the actual proportions to mix the soduim hydroxide. The aluminum should fizz when it is put in.
I usually only mix 1/2 gallon of each particular dye, unless I am doing a larger part that needs more dye. I keep it in the jug the distilled water came in and put it in the crock pot when I need it.
from left: sodium hydroxide, sulfuric acid, baking soda and water, crock pot for heating dye, behind that a small burner with pot of distilled water for sealing. If I am doing a larger part I will use a bigger pot on the kitchen stove to seal it.
top shelf: dyes and rectifier
not pictured: rinse water
Anodizing process:
Before anodizing, the part should have the desired surface finish. Anodizing will not hide a poor finish. Often I sand my work to 400 or 600 grit then use a green scotch brite pad for the final finish. Other finished I have used include polishing, file texture, and sandblasting.
The metal must be very clean and grease free before anodizing. I use an ultrasonic cleaner with a degreasing solution. Before I had an ultrasonic I used Dawn dishwashing soap and a toothbrush. After the part has been cleaned I try to avoid touching it, and if I do need to touch it I make sure I have washed my hands well or I wear latex gloves. Having a clean part is the most important factor in getting good results.
Usually it is recommended to etch the part with caustic soda prior to anodizing to clean it, but I have found this is not necessary.
Before putting the part in the anodizing bath I turn on the crock pot with the dye so it will be heated by the time I am ready to use it. I also start heating the sealing water.
The part to be anodized must be attached to bar receiving the positive current using an aluminum wire. The part must have a good connection, it can't just hang by the wire. The way I most often attach the wire is to drill a small hole on a hidden spot on the part, the same diameter as my aluminum wire, then use pliers to force the wire into the hole. As long as the part isn't too heavy and there is a good hidden spot to drill the hole this method works well. However you attach the wire, the spot where the wire touches will not anodize. The larger the part the heavier gauge wire you need to use to attach it. It needs to be able to handle the current. Sometimes I use more than one wire. Since I have an ultrasonic cleaner, I clean the part with it again after attaching the wire. If you have cleaned the part by hand, you may want to wear latex gloves when attaching the wire so you don't get the part dirty with your filthy hands!
I have also made small mandrels to hold parts. This mandrel was turned on a lathe with a slight taper then forced into a hole on the part.
To attach the part to the rod I use either a small c-clamp or a spring clamp. Again, the connection has to be good.
Turn on the rectifier and adjust the volts to 12v. Don't worry about the amps, the larger the part the more amps it will take. Most of the small things I anodize are at about .5 - 1 amp. Tiny bubbles may come off the part, This seems to vary depending on the alloy. Some alloys have a constant fizz coming off of them. Others have almost none. I anodize the part for an hour.
The next steps shoud be done immediately after the part comes out of the anodizing bath. At no point should the part be touched or allowed to dry. After an hour turn off the rectifier, remove the part and submerge it in baking soda water to neutralize the acid. I usually move the part around in the water for about 10 seconds. After this, rinse in distilled water, then put the piece in the dye. The amount of time the part should be in the dye depends on how dark you want the color. How quickly the part accepts the dye will depend on the alloy, the amount of time it has been anodized, and the concentration of the dye. I have had some pieces in the dye for only a few seconds to get the color I wanted, others I have left in the dye for 15+ minutes to try to get the darkest color I could. Sometimes if you leave the part in the dye for a long time it comes out with a velvety look to it, it looks cool, but it will come off when you touch it.
After dyeing the part is sealed using hot distilled water. I have heard the water should be 190 degrees F, I usually just heat the water to near boiling and don't worry abot the exact temperature. Leave the part in the hot water for about 20-30 minutes. After that I usually wax the part with Renaissance wax or Johnson's paste wax. Waxing the part sometimes evens out uneven color. There are also chemical sealers to seal the part. I don't have any experience with them.
If you are happy with the color then thats it, you're done. If you are not happy with the color it can be removed with caustic soda. Some of the color usually stays on while its in the caustic soda, but it wipes right off. So you may want to take the part out, rinse it and wipe off the residue to speed things up. Length of time in the caustic soda depends on its concentration. Mine usually doesn't take more than 20 minutes. Don't forget your part is in the caustic soda, and leave it in there for a week untill you are looking for it wondering where you left it and finally remember it was left in the caustic soda, but it has been totally dissolved and now you have to remake the part! I'm not talking from experience or anything, really.
You can also sand the anodizing off, but I don't recommend it because its a pain in the donkey.
Note in the above photo, the piece on the right, the hole the wire was in is not anodized.
I recommend to anyone who is planning to give it a try to consult more sources online. Some people do things differently, I am just showing you how I do it.
www.mcmaster.com - lead, buckets & lids, aluminum
www.caswellplating.com - anodizing dyes
hardware store - sulfuric acid (drain cleaner), sodium hydroxide (drain cleaner)
