At one shop that I worked at, we’d regularly send things out to be heat treated, anodized, zinc-plated, galvanized, you name it. If you wanted anything done for a personal project, just put it on the pile and be patient.
Unfortunately, I no longer work at this shop. Where I am now, it’s actually pretty rare that we’ll get something anodized. So for my own little projects, I did some research on how I could pull this off at home in my garage.
I found the information to be really scattered. That’s why I compiled what I learned into this one article. This should be pretty well all you need to get started.
In this post, I’ll share what I’ve learned about how to pull this off successfully, as well as a few tips and tricks to help you along.
Disclaimer: I have done this professionally, but doing it at home is another animal entirely. Expect it to take a few tries before you get the process right.
What Does Anodizing Aluminum Do?
It’s probably a good idea to start off this guide by making sure you understand what the process is. This will help you to understand what’s going on and why it’s important as you go through the steps.
What does anodizing aluminum do? Anodizing aluminum creates a thin layer of aluminum oxide on the metal. This protective oxide layer has a rougher surface that allows dyes or paints to stick to the metal. It is harder than aluminum, so it offers a measure of protection. It also gives the aluminum corrosion resistance. Since it’s such a thin layer that oxidizes, it can be done to precision parts with minimal effect on geometry.
It’s also commonly done for cosmetics even on parts that won’t be dyed or painted. Anodizing gives the aluminum a dull light gray color. It also won’t corrode from things like the salt on your hands, leaving cloudy marks over time like bright aluminum will.
What You Need
The anodizing process itself isn’t terribly complicated, and it’s not too expensive to set up (I know, everything is relative).
This is what you need to anodize aluminum:
- A power source with connections
- Distilled water
- A cathode
- A container
- Dye (only needed if you want to make it a different color)
- Aluminum or titanium wire
- A degreaser
- An acid neutralizer
- An agitator (optional)
- Safety gear
- A ventilated area to work in
A lot of this stuff can be scrounged, but some things work better than others. I’ll go over some options for what can be used here to help you set a budget. At least you’ll know what to expect, and you won’t waste your money on things that won’t work.
Small-Scale Anodizing Setup
If anodizing is something that you’d like to do fairly often and you don’t mind dropping a bit of money, then this is something that makes sense.
Complete kits can be tricky to find online, sometimes you’ll need to buy the items separately.
Here’s a quick run through of what’s available. If this isn’t what you’re interested in, then just skip down to the next section about the more DIY approach. Spoiler: the DIY route will give you a very mixed bag of results.
Note: Online prices fluctuate, so I could write this article today, and tomorrow they’re different. I did my best to give a pretty good idea of what these things go for, but don’t hold my feet to the fire on this one! The budget is at the end of the gear section.
In general, you’re looking for something that can put out around 18v and up.
Amperage is important based on the amount of surface area on the part you’re wanting to anodize. This is a little easier to balance, though, since you can compensate by simply running it for longer. Either way, you’ll probably want at least one amp for smaller doodads and widgets.
You can find decent power sources online for around $60-100+. The perk is that these power sources are versatile – you can use them for other things like plating too.
This is the one that I’d recommend picking up. It’s 30 volts and 5 amps, so it’ll cover you for most projects that are in the neighborhood of one square foot of surface area. It’s also got some nice alligator clips that make life easy for projects like this.
As a rule of thumb, you need roughly 0.02 to 0.03 amps per square inch of part surface area.
If you want to MacGyver your setup, you might be able to get away with using a larger car battery charger. The advantage to this is that you might already have one that’ll work. The disadvantage is that you don’t have anywhere near the same amount of control over the power, you’ll have a hard time fine-tuning your process to get everything right. Anodizing can be fussy.
The most common acid that you’ll see in garage setups is sulfuric acid. You can usually find it for around $40 for around a gallon and a half.
Pro tip: Battery acid is essentially sulfuric acid, it just probably also has a few additives. For our purposes, it works just fine. You can usually get it for a little cheaper than the lab-grade stuff. Here’s an example on Amazon of something that will work.
This is optional, but using a really strong acid can be a good way to prep the aluminum and remove any oxide that might be on it. Lye works great and it’s cheap. You don’t need a lot of it.
Lots of online resources say to just use fabric dye if you want to color an anodized part. Based on my experience, this usually works as desired, but not always. Sometimes the colors are really off – blue can look purple, purple can look pink, etc.
If you’re not too fussy, though, clothing dye is pretty cheap. You can usually pick it up for a few bucks online.
If you want to make sure that this works as expected, just pick up some proper anodizing dye. Here’s an example of one that’ll work great. Good dye usually costs around $20 or so for a bottle, depending on where you get it.
Technically you could just use a piece of aluminum for this, but lead works better and lasts pretty well forever. I’ve gotten the best results using sheet lead since it has so much surface area.
You can just pick up some lead flashing from a home center, or you can pick up a little sheet on Amazon. This’ll basically be a one-time purchase since lead doesn’t really deteriorate.
Plastic containers work great. You don’t need to overthink this. For medium-sized or larger parts, just use a 5-gallon HDPE pail that’s nice and clean. For really small stuff, you can use a tupperware container or even a glass mason jar.
Just pick something that doesn’t conduct electricity and that can resist acid.
You can use aluminum or titanium wire to hold the part. I strongly prefer using titanium. Here’s why.
The racking needs to be able to conduct electricity very reliably. Aluminum oxide doesn’t conduct electricity.
What this means is that if you use aluminum wire, the wire will get anodized too. Titanium won’t. So not only is the titanium wire reusable, it’s also less likely to lose the connection during the process.
Either way, though, both wires will work, and they don’t cost much. You can pick up titanium wire (a little more expensive)or aluminum wire (cheaper). Honestly, if you’re planning on anodizing a few pieces, just pick up the titanium wire.
Nothing to overthink here, just something that will get any grease or oil off the part to make it nice and clean. You might already have something good in your garage. This will work great.
Use baking soda. Works like a charm.
This is optional, but it’s a good idea. Basically what happens is this will prevent bubbles from sticking to the part during anodizing and leaving little marks. If you want the parts to look pristine, there’s a simple but extremely effective hack.
Use a fish tank air pump. If you can’t “borrow” one out of your kid’s fish tank for a while, you can check a current price on Amazon here.
This is important. You’ll need eye protection, a respirator mask for chemicals and gloves.
I’ve seen a lot of people use just a plain dust mask when doing stuff like this. I really wouldn’t recommend this, since dust masks don’t stop fumes, only particles.
This is a mask that works well, it’s not too expensive, and it’ll do something against fumes. It also comes with some safety glasses, in case you don’t already have a pair. Getting acid in your eyes sucks.
It’s not that the fumes are hyper toxic, but it’s a good idea to avoid breathing them in.
You’ll also need a pair of gloves. I prefer nitrile, and you can get a box for not too much at all. This isn’t just to protect your hands from acid burns, but also to keep oil off the part. If you touch the part with your bare hands, you’ll have permanent fingerprint marks after anodizing.
Miscellaneous Handy Stuff
There are a few things that aren’t necessarily required, but really do help you to do a good job.
Ping pong balls can float on top of the acid mixture. This is pretty well eliminate the acid mist that you’ll get when the tank starts to bubble during the process. You can buy a pack of 50 online that will last an anodizing lifetime.
Scotch brite pads are a good way of making the surface finish nice and even before anodizing. Not required, but if you’re anodizing machined parts, all the marks will show through. This just makes the part look a bit more professional. You can buy a large pack of these that will last you a while with a great bang-to-buck ratio. I use this stuff all the time for different projects, so I always have a stash on my shelf.
A tea kettle for heating up the dye (if you’re wanting to color the parts). Most dyes need to be at around 120-140 F or so when you dip the part in, and using an electric tea kettle makes this step really easy. You can pick up a cheap one on Amazon. Just don’t use it after for making tea.
A fish tank heater will let you regulate the temperature in the tank. You want it to be as close to 70F as possible. If you’re doing this in a temperature-controlled area, this isn’t critical. If you’re doing this in an unheated garage, I’d highly recommend it. You can check the price on Amazon here.
A meat thermometer will let you be sure of your temperatures. It’s also really handy for checking the heat of your dyes. Not required, but a good idea. You can get one for cheap online.
The Grand Total
Chances are you probably have a fair bit of this stuff in your garage or you can scrounge. But in case you have to buy absolutely everything new, here’s a breakdown of what to expect if you pay a pretty average price for everything.
|Fish Tank Air Pump||$10|
|Respirator and Safety Glasses||$25|
|Box of Nitrile Gloves||$10|
|Ping Pong Balls||$10|
|Pack of Scotch Brite Pads||$20|
|Fish Tank Heater||$15|
|Distilled Water (locally sourced)||$5ish|
Now, keep in mind, this is if you need to buy everything. A reasonable amount of this stuff is optional, and you could also buy it in smaller quantities if you want. But starting from scratch, this is a setup that will allow you to do really good quality anodizing from your garage. Lots of guys use setups like this to make parts that they sell online.
Once you’re all set up, it’s not very expensive at all to maintain your system. You’ll need to top up with acid, lye, dye, degreaser, baking soda, gloves, and scotch brite, but you really don’t use all that much. This stuff will last you a while. Anodizing isn’t an expensive process once you have the gear.
How to Anodize Aluminum the DIY Way
Ok, so once you’ve got all the stuff, here’s the step-by-step instructions on how to do this.
Keep in mind that every setup is different, and you’ll need to fine tune your process to get the results you want. Don’t expect it to come out perfect the first few times.
Scotch-Brite the Aluminum
This will give a nice, even surface finish that will look good after anodizing. It’s not totally required, but it seriously does make the part look more professionally.
If you don’t scotch-brite it, the machining marks will be clearly visible. The part will be shiny in the areas that have a nicer surface finish, and dull in the areas where it’s not perfect. It’s just more noticeable after anodizing.
Don the Gear
Get your respirator within hand’s reach. Put on your safety glasses. Most importantly at this step, wear the gloves!!! If you don’t wear gloves, you’ll leave fingerprints on your part and your anodizing will look terrible.
Clean the Parts
Get out that degreaser and some clean cloths. The surface of the part needs to be perfectly clean. Rinse the part of with distilled water when you’re done.
Etch the Parts
Get out the lye and mix it with distilled water. The ratio is about 3-5 tablespoons of pure lye to 1 gallon of water. Make sure you’re wearing your respirator and safety glasses at this point, lye can be nasty stuff.
Let the part soak for 3-5 minutes, then rinse it off with distilled water.
At this point, you can do a water test on the part to make sure that it’s cleaned properly.
If you cleaned it properly, water should smoothly run off the surface of the part. If you messed up, the water will bead on the surface. This is because there are still oils on the surface. In that case, repeat the cleaning process.
This step is really important. Anodizing will only work on a really clean part.
It’s absolutely imperative that you don’t let the part come into contact with anything dirty at this point onward. Wear gloves throughout the process, and don’t put the part down on a dirty surface.
Rack the Parts
Secure the parts to your aluminum or titanium wire. Keep in mind that there will be an unanodized mark left where the wire was contacting the part.
Most guys like to use the inside of a hole as a contact point so it’s not really visible. One neat little trick is to ball up the end of the wire and shove it into the hole. The springiness of the wire will hole the part in place, and you’ll have no visible marks on the anodized surface.
One thing that’s critical: You need a good connection. If the connection is loose, the process is guaranteed to fail. Since aluminum oxide doesn’t conduct electricity, you’d have to pull out the part, sand away the anodized surface, and restart the process. It’s a pain.
Pour the Bath
Put your container in a well ventilated area. Anodizing works best when it’s done at around 70 F. If needed, give your liquids time to acclimatize. Anodizing at a temperature over 75 degrees won’t give very good results.
Pour the distilled water in the container first. Then add the sulfuric acid. The ratio is 1 part acid to 3 parts water. I know other websites say to do half and half. They’re wrong. The acid shouldn’t be that strong. This concentration works better and it’s cheaper, too.
Always pour acid into water, not water into acid. The burns can be nasty if you mess this up.
Set up the Gear
Put the lead cathode in the bath. It’s really important that it doesn’t touch the parts. I like to have it wrapped around the inside of the bucket to give a nice, even oxide layer on the part. No clue if it actually makes much of a difference or not, but it’s what I do.
Put the air pump right under where the parts will be. The more agitation around the parts, the better.
Put your heater and thermometer in the tank. Make sure the bath is as close to 70 F as possible before starting.
Suspend the parts in the tank. I usually just put a piece of flat bar over the bucket and hang the parts from it. Make sure they’re not touching anything!
If you decided to get the ping pong balls, this is where you can add them. Add enough to cover the surface of the acid mixture.
Set up your power supply. Attach the positive side to the wire on your parts. Attach the negative side to your lead cathode.
Hint: The parts are your anode, the lead is the cathode. Anodizing = parts are anodes. Parts are always positive.
Once everything looks secure, it’s time to fire up your power supply. This is where it gets fussy.
You want to set the amperage based on the amount of total surface area on your parts. Using 0.03 amps per square inch will give a nice hard surface, using 0.02 amps per square inch will give a softer surface, but it’ll take on more dye. Either way, it’ll take a little experimenting to make this look exactly how you want it.
Try running at 16 volts to start. Really, there are a whole bunch of calculations that you can do to get this theoretically perfect, but this is a beginner’s guide. This’ll get you close enough to start. Besides, there are a few other variables that affect the calculations that are really tricky to get perfect with one of these home setups.
So here’s a really simplified calculator I made up that works well for me when I’m doing this at home. Keep in mind that this is not what I use at work for professional controlled aerospace anodizing, but it does seem to work pretty good for these more home-made setups.
One thing that’s a good idea (at least it’s good practice) is to slowly turn up the amps. This is what we do professionally – it’s pretty common to have a 5 or 10 minute ramp up when starting a batch. You don’t need to go this slow, but just don’t instantly crank the power – take your time turning that knob up.
Set a timer for whatever number that calculator gave you and go take a coffee break!
Pro Tip: If you’re anodizing a few parts or one larger part, keep an eye on the temperature of the bath. It can warm up if it’s working harder. If you see it getting up to 75 F or higher, try doing something to keep it cooler.
You’ll also want to make sure that it doesn’t go under 60 F. This is where that fish tank heater comes in really handy.
Heat Up the Dye
Get out that tea kettle and warm up the dye, checking the temperature with the meat thermometer. This can be a bit of a fussy step.
Most dyes work well at around 140 F, but some colors perform slightly better at a lower temp, like 120 F. I’d recommend trying the first batch at 140 and if you’re not happy with the results, try the next one a little cooler.
Get your Baths Ready
Ok for this step we’re going to set up a couple of baths. I know other people may to this step differently, but this is what works for me.
Set up one tub of distilled water. It’s good if it’s a fair bit larger than the parts. For example, if you have a part that’s as big as your fist, use at least half a gallon of distilled water.
Put some distilled water in a spray bottle. Not mandatory, but it’s handy.
Next set up one tank with a mix of baking soda and distilled water. This will neutralize the acid and make it more likely that there won’t be any blemishes on the parts. I’ll usually use a ratio of 3 tablespoons of baking soda per quart of water. There’s nothing sciency behind this, it’s just what I do. You don’t need a ton of this mixture, just enough to cover the parts so they can soak for a few minutes.
Then open up the lid on the kettle with the dye in it. You can just dip the parts in directly.
Turn off the power to the anodizing tank. Lift the parts partially out of the tank and give them a few sprays of distilled water. I spray down directly into the tank so it doesn’t make a mess.
Now swish the parts around in the distilled water tub. You just want to rinse off as much of the acid as possible.
Then put the parts in the baking soda tub. Swish it around a bit and let it sit for around 5 minutes.
Now rinse off the parts again in distilled water. Be thorough.
Double check the temperature of the dye and adjust as needed.
Dunk the parts in the dye. Stir it around vigorously enough to knock off any bubbles on the parts, but don’t make a massive mess. This stuff is a pain to clean.
You should be able to see the parts instantly start to take the dye. If the process didn’t work, the dye will just drip off. If it did work, the part will start to change color. Let the parts soak in the dye for 10-15 minutes.
Later on you can fine tune this soak time depending on how deep of a color you want.
This part is really easy. Once the soak in the dye is done, boil the parts for about 15 minutes. This is where it’s handy to have either an extra kettle or a hot plate where you can boil a pot of water.
This will just toughen up that dye and make it less likely that the dye will discolor or easily come off. Even if you didn’t dye the parts, this is a good idea.
There you go, the process is done!
Overall, I really like doing anodizing at home. It will probably take a little bit of practice to get parts that are properly anodized and without blemishes, but it’s a really cool process.
It’s also a lot of fun to fine tune and tweak how you do it so that you can get the exact look that you want – there are a bunch of variables and each one affects how the part looks in the end.
Have you tried anodizing? What were your results, and is your process different from mine? Or do you have any questions? Post them in the comments!
What is hard anodizing?
Hard anodizing is a process that uses higher current and is done at a lower temperature. The result is a considerably thicker oxide layer, often around 0.002″ thick. This layer is extremely hard and can significantly increase the wear and corrosion resistance of aluminum. The requirements for this process are much higher, and not all finishing facilities have this capability.
A point to consider with hard anodizing is that since the oxide layer is so thick, it will cause noticeable dimensional changes in precision components.
How much does professional anodizing cost?
To get something professionally anodized, there will be a minimum charge, a price per square inch of surface area, and possibly a racking fee. Of course, this is going to vary a lot by location and facility, but you can expect anywhere from $75-125 for a smaller batch. A good rule of thumb for the definition of “small batch” is anything that you can carry in a box. Truckload = probably not a small batch.