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Guide Anodizing and Etching Aluminum

Discussion in 'Modding' started by ChromAnomaly, 22 Nov 2013.

  1. ChromAnomaly

    ChromAnomaly What's a Dremel?

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    Based on a couple requests from my latest scratch build, Behemoth, here is a basic primer on anodizing and etching aluminum.

    Why Anodize?

    Spray paint works just as well, right? Well not exactly. Anodizing embeds dye molecules in to the surface of your aluminum, whereas painting just coats the surface with a cheap pigment impregnated polymer. That means paint scratches, chips, and fades over time. Anodizing is permanent. The only way to take this stuff off is with concentrated NaOH.

    If that's not enough for you, anodizing maintains the exact same surface qualities of the original metal. Want a brushed finish? No problem. Want a high gloss sci-fi colored metal that doesn't exist in real life? Anodizing can do that.

    And c'mon, what's cooler than chemically treating your computer case with concentrated acid and a car battery charger? :rock:

    Anodizing Setup

    First thing is first, make sure your aluminum is SPOTLESS clean, and has the finish you want. You can't polish or shine this stuff after anodizing, and the process will dull the finish slightly. So always err on the side of higher gloss than you want in the end.

    Speaking of spotless, no fingerprints, grease marks, dust, scratches, etc. Use gloves. Polish up your aluminum, put on some gloves, and wash it with soap and water. Scrub it with a polymer brush (like a pot scrubber). Don't come anywhere near it with steel wool or a brillo pad though. Those tiny fibers of steel will embed themselves in the aluminum and completely ruin the anodizing process. It is absolutely critical to keep all other metals away from your aluminum. Also, once you scrub down your aluminum, keep it under water until you start anodizing. Aluminum forms a layer of oxidation on the surface VERY quickly, and keeping it submerged at after scrubbing makes sure you maximize the amount of available aluminum on the surface.

    You can anodize "any" aluminum, but 6000 series alloys are easy to find and work well. Many other alloy series have various levels of other metals in them which will screw up the anodizing. The quickest way to screw up your anodizing is to contaminate your acid bath. Once you get a tiny bit of another metal in it, forget it - you'll need to make up a new solution. Some aluminum alloys need to be de-smutted before anodizing (to remove other metals from the surface), and I still haven't found a great process for that. Luckily most aluminum you find at the hardware store, etc is a 6000 series alloy.

    Here was my first anodizing setup. It didn't work great, as the PSU doesn't put out enough amperage to drive the process. Also, the aluminum foil isn't the best material to use for a cathode as it can also have contaminants. But it did work, more or less. So this is all you really need for anodizing.
    [​IMG]

    A bit more advanced, but still quite easy and inexpensive. Here I have a rather large plastic tub (for anodizing large sheets), a car battery charger with 50 amp output (about $30 on Amazon), and a couple scrap strips of aluminum from the hardware store to use as cathodes. Note that I now have 2 cathode strips instead of just 1 - this helps balance the charge in the solution.
    [​IMG]

    A note on plastic tubs. The dimensions listed for the tub are usually the exterior dimensions at the top of the tub, which makes the number quite useless for determining whether or not you can submerge a sheet of metal in the bottom of the tub. Be sure to go to the store and measure before buying. And try to avoid anodizing anything larger than 9" across - finding tubs that big is a huge pain.

    One other thing to keep in mind, the last step of anodizing is to boil the part in water for 30min. You can also steam the part over a water bath, but this tends to leave streaks in the finish. So try to limit your part sizes to the largest scrap broiling pan you can find to stick in your oven.
     
  2. ChromAnomaly

    ChromAnomaly What's a Dremel?

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    WARNING - This guide recommends playing with dangerous chemicals and open electrical currents. Wear gloves, goggles, and old clothes. And for the love of god, don't touch anything! Keep lots of baking soda around to neutralize acid spills, and absolutely do not dump this stuff down the drain.

    Anodizing Ingredient List

    • Aluminum to anodize (preferably a 6000 series alloy)
    • Aluminum cathodes (preferably a 6000 series alloy. I hear lead will work too, but no other metals)
    • Wire leads (preferably aluminum, ~12 gauge)
    • Battery charger capable of 50amps (Amazon, ~$30)
    • Sulfuric Acid (H2SO4 or NaHSO4). You can use car battery acid if you can find it, or look for "pH Down" in a local swimming pool supply store. The rest of this guide assumes you found pH Down (which is NaHSO4). It's a bit less potent than H2SO4, but it's a pure solid as compared to car battery acid which is already made up in to a 20% solution
    • Aniline dye, aka RIT fabric dye. Any brand of fabric dye should work. Find it at Walmart or the grocery store.
    • 2 plastic tubs large enough to submerge your aluminum parts.
    • 1 oven-safe pot / pan large enough to submerge your aluminum part. Alternately, any other container you can get boiling water in to and keep it hot for 30 min while submerging your part.

    Anodizing Instructions

    • Mix up the acid (NaH2SO4) in to a 20% solution. That's 40g in 200mL of water, or about 25 TSP in 8 cups of water, etc.
    • Bend two strips of the scrap aluminum and place one at each end of the container with the acid solution. You want at least as much surface area of aluminum submerged as your part has surface area, and then a tail of aluminum sticking up out of the acid to connect your wire leads to.
    • Wrap some wire around each scarp aluminum tail and connect them together. This wire is your cathode, and will be hooked up to the negative (black) lead of the battery charger.
    • Let the acid sit for a bit while you construct an aluminum wire rig to suspend your part in the solution. You don't want any surface of your part to touch the container, and you have to have the entire part submerged. You need good electrical contact between the wire rig and the part, but any surface of the part in contact with the wire will not get anodized. Your best bet is to wrap the wire rig (tightly) through holes in your part.
    • Submerge your part in the acid using the wire rig, and connect the positive (red) lead of the battery charger to the wire rig. Make sure all of the charger's parts are well clear of the acid solution (that's what the scrap aluminum and wire rig are for!).
    • Turn on the charger and look for bubbles. Bubbles should be coming off of your aluminum part, not just the wire rig. If you don't have bubbles on your part, something isn't connected right. TURN EVERYTHING OFF before troubleshooting. There should be more bubbles on the scrap aluminum (cathode) than on your part (anode).
    • Leave it be for an hour or so. The time you need to anodize will depend on the size of your part, and the amperage your power supply is putting out. When you stop seeing bubbles on your part, you're about halfway done. The part should also get a bit of a dull yellow haze on the surface, though I have a hard time seeing this. I've had tiny parts anodize in 30min, and large parts require up to 4 hours. Don't leave it in too long though, or you will end up with something like this:
      [​IMG]
    • In the meantime, mix up some dye. Follow the directions on the clothing dye, but make it about 2x the recommended strength. Don't bother with salt or vinegar if it recommends that. You will want to heat this stuff up to about 140deg F though. For a small plastic container, you can toss it in the microwave until it's just about to boil. Take it out and let it sit for a few minutes. You want to make sure it's hot but NOT boiling.
    • Unhook the charger and remove your part from the acid. Rinse it thoroughly in cool clean water, making sure not to drip anywhere or touch the part directly.
    • Submerge your part in the dye. You'll want it to sit for 10-30min depending on how colored you want the part. Check it from time to time.
    • While the part is being dyed, get some clean water boiling. An old pot on the stovetop works great for small parts, or a broiling pan in the oven works for sheets. You can steam the part instead of boiling, but this is a real pain and often results in streaks in the finish.
    • Remove the part from the dye and submerge in boiling water for 30min. You will lose a little bit of color during this process, so err on the side of a darker dye job. If the dye doesn't take, or washes off in the water, your anodizing process failed. Sorry, try again.

    Anodizing Examples

    Small blue dyed aluminum strip. The original aluminum strip is in the background for comparison. I sanded the strip a bit prior to anodizing it, thus the rough surface.
    [​IMG]

    Computer case plate, brushed aluminum, purple dye. Note the somewhat cloudy finish, which is due to steaming the plate instead of immersing it in boiling water.
    [​IMG]

    Motherboard tray, brushed aluminum, purple dye with a bit of blue (yes, you can mix dyes!). Again, a few streaks and splotches dues to the steaming process.
    [​IMG]

    Anodizing - What if I Screw Up!?

    Don't worry, you can remove the anodizing with a bit of NaOH. Also known as lye (you can get this from Amazon, or the grocery store). Mix a 2% solution (4g in 200mL water, or ~9 TSP in 8 cups of water), and submerge the part for a few minutes. You'll see the anodized layer strip off. You can also use this with an aluminum part that you bought already anodized. NaOH stripping will leave your part with a dull finish, which can create an interesting look when anodized . . . but if you want it shiny you will need to re-polish it after this step.

    Be sure to rinse the part well in water after a NaOH soak before doing anything else. You can neutralize NaOH with vinegar, so keep some of that around your lab :)
     
  3. ChromAnomaly

    ChromAnomaly What's a Dremel?

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    Why Etch Aluminum?

    Etching aluminum is a great way to create a permanent design on metal. It's much cleaner than simple engraving, and can create a wider variety of line widths and depths. This same process also works for copper or zinc, and is the way printing plates used to be made.

    And of course, what could be cooler than using acid to dissolve away parts of your metal case, leaving your design permanently etched in to the surface? :rock:

    Creating an Etching Design

    Etching is great and all, but it's only useful if you can etch part of your metal while leaving the rest unaffected. People have used all sorts of materials to "resist" the etch, but most of them do a crap job and will leave you disappointed. You can use paints, nailpolish, or even a sharpie marker to draw your design, but in all likelyhood these resists will start to dissolve after a few minutes of etching. This results in sloppy lines, or at best a shallow and unimpressive etch.

    For simple designs, packing tape (the clear plastic stuff) actually works quite well. Lay the packing tape on your metal surface, and cut out your design with an exacto knife. Or cut the tape in to shapes prior to applying. Be careful if you cut the tape after laying it, as your knife will score your metal. The only problem with packing tape is that fine lines and details will start to lift up, allowing the etchant to get underneath. Tape is best used to block off large areas with straight edges that you don't want etched.

    The best resist by far is asphalatum . . . but it's a real pain to work with and can be hard to find. Luckily I found this amazing stuff called Univeral Etching Ground (Hard Ground) which is basically asphalatum in a liquid solvent. Paint a thin layer of this stuff on your surface and let it dry for a few minutes, then repeat 2 more times. Stick it in the oven at 300deg F for 30 min to evaporate the solvent, and you'll have a completely chemical resistant surface (you can remove it with paint thinner though, and it's still scratchable).

    Once you have a baked asphalatum surface, you can scratch your design in to the surface. Alternately, you can paint the negative of your design on to the surface instead of coating the surface, but I found this difficult to control since the etching ground solution is pretty thin. However you do it, you should end up with something like this:
    [​IMG]

    Make sure every surface of your metal (sides, back, etc) are coated in resist where you don't want to etch.

    Etching - The Fun Stuff
    To etch metal, you're going to want to pick up some FeCl (ferric chloride). You can pick it up on Amazon, or at art supply stores . . . but that's about it. I've tried a number of other etchants, but nothing else really works. FeCl is a little pricey, and it's kind of nasty stuff, but it's worth it.

    You're going to want to suspend your part face down in the FeCl. During the etching process, a lot of precipitate comes out of solution, and you don't want this stuff to deposit in to your etch. The easiest way to do this is to put a piece of packing tape across the back of your part, and tape it to the sides of your etching container. You can also use double sided tape to tape the part to a piece of styrofoam and float the part in the etchant.

    In case you're wondering what the process looks like face up, here you go. This is a fairly violent reaction and produces a lot of heat. I melted the plastic container under my test sample because it was in direct contact with the aluminum part. This shouldn't be an issue if you suspend the part in a solution.
    [​IMG]

    Here's the end result after 3-5min of etching, removing, rinsing, and scrubbing off the resist with paint thinner. If the etch lines get much thinner than this, the etchant beads up on the resist and cant get to the metal. Thin lines will eventually etch after about 30min in etchant, but at that point the resist is starting to deteriorate and things get messy. Bold lines, and a good balance between resist area and etch area give the best results.
    [​IMG]
     
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  4. jamsand

    jamsand Minimodder

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    fantastic guide just scared of blowing myself up lol
     
  5. ChromAnomaly

    ChromAnomaly What's a Dremel?

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    For what it's worth, there are relatively few ways to literally blow anything up in this process. Just don't try to anodize or etch in a sealed container. But electrocution and chemical burns are definite possibilities if you're not careful, and having adequate ventilation is really important.

    Really I think this stuff is much less dangerous than using power tools. Where people get in trouble is when they stop respecting what they're working with. If you stop respecting the danger of your table saw, you're probably going to cut a finger off. Because chemicals and electricity are more or less invisible, it's easier to forget that they are dangerous.

    Either way, thanks for reading :)
     
  6. GuilleAcoustic

    GuilleAcoustic Ook ? Ook !

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    Great guide mate, this should definitly be stickied !
     
  7. jrs77

    jrs77 Modder

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  8. ChromAnomaly

    ChromAnomaly What's a Dremel?

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    Lots of websites sell kits, but usually they are quite a bit more expensive. And note that the kit you link to does not include the sulfuric acid or the power supply, which happen to be two of the more difficult (and important!) components.

    Personally I would skip the NaOH (it dulls the finish), and the aluminum cleaner is completely unneccessary if you've sanded / polished the part (which you should do anyway) . . . so really they are selling you $15 worth of dye for $65.
     
  9. ChromAnomaly

    ChromAnomaly What's a Dremel?

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    Thanks! And sorry I missed your reply somehow :duh:
     
  10. jrs77

    jrs77 Modder

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    Battery-acid is actually dirtcheap, aswell as distilled water and a small 12V / 2Amp PSU. For small stuff like I'm intending to anodize you don't actually need a regulated PSU with lot's of power.

    For experimenting with this stuff, €40 is not that expensive imho.
     
  11. ChromAnomaly

    ChromAnomaly What's a Dremel?

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    The price is good for a kit, and if you can get battery acid easily then go for it . . . but you'll need a lot more than a 2 amp PSU no matter how small the part in my experience. I use a 50 amp battery charger which works well, but the computer PSU at ~12 amps can barely handle anodizing a 12cm^2 part.

    You can pick up a 50amp battery charger for around $50, but just make sure you add that in to the cost of your setup. And seriously, the only other thing you need is a $5 bottle of clothing dye and the instructions I already gave you . . . but whatever, suit yourself if you want to go with the kit.
     
  12. jrs77

    jrs77 Modder

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    Rule of thumb for the current to anodize should be 150-175mA per sq in (6,45cm²), or 1.5Amps for 10 sq in (~65cm²). So 2 Amps should be enough for most small parts like a 18650 battery tube. And I'm not going to anodize anything larger.
     
  13. ChromAnomaly

    ChromAnomaly What's a Dremel?

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    I've read that too, but I could never get it to work well at low total amperage. The car charger I'm using anodizes parts up to ~7500cm^2 (that's only ~45mA/sqin) with no problem, and does the small parts as well without damage (13,000mA/sqin). But using a 12Amp source and a 24cm^2 part (3000mA/sqin) resulted in acid pitting before I could get it to anodize.

    I know I didn't have a perfectly single variable experiment there, so perhaps you'll be able to get it to work at low amperage. I would imagine the volume of the acid bath and size of the cathode also play a role. Either way I'd be curious to see how it turns out. Good luck! :dremel:
     
  14. jrs77

    jrs77 Modder

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    I watched several videos about this, and there was this one guy using a 12V 2 Amp PSU for anodizing his selfmade pens without any troubles.

    I'm looking at some 1 liter of acid-bath to anodize the parts in, which have a combined surface of a pack of cigarettes, so it's really small and the 12V 2A PSU should work just fine.
     

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