Small Scale Aluminium Anodising in the Home Workshop

Small Scale Aluminium Anodising in the Home Workshop

Hello! First off let me just say this isn’t meant
to be any kind of anodising “how to” it’s more of a “what did”. I’m not any kind of expert. I’ve only done maybe a
dozen small parts over 3 years or so. Whilst I was getting the stuff together to
have another go, I thought I’d share my experience from a UK perspective,
as a lot of what’s out there is by US authors. This is the piece I’m going to anodise it’s going to be part of a puller I’m working on. I’m not sure what grade the aluminium is,
and it remains to be seen how well it’ll work. The first thing to say is that unlike painting
or other coatings, anodising won’t hide anything. If your part’s not perfect,
but you’re happy with it, carry on. But remember the way it looks
now is the way it’ll look in the end. I’m aiming for a satin brushed look for this part. Here I’m using 400 grit wet & dry
and a bit of WD40 to bring all the surfaces to a similar looking finish. I’ll put the part to one side for now and
wash my hands. I knew I’d left the gloves out for something… Before I do anything with any chemicals
here’s the disclaimer: Sodium hydroxide and sulphuric acid
can both be very dangerous. You need a tidy space to work, gloves,
eye protection and old clothes. Trust me on the old clothes.
The acid’s cost me two pairs of jeans so far. When making up the solutions
always add the chemical to the water not the other way round. There’s various confusing rhymes out there, that are supposed to help you remember this but this is how I see it: Chemicals are dangerous. Hungry sharks are dangerous. Think of the chemicals as hungry sharks. A drop of water into a tank of
concentrated chemicals is like a drop of blood into a tank of
concentrated sharks. They’re going to go berserk! Possibly covering you in a shower of boiling sharks. On the other hand if you drop one shark into a tank of blood,
you’re probably gonna be ok. I’m using deionised water for this film. I’ve used reverse osmosis water, and that worked fine. I’ve not tried distilled. Some people reckon soft tap water’s good enough. I usually use an etch bath made
with 2% sodium hydroxide. This is fairly easy to get hold of and can usually be found
in the cleaning isle of the supermarket. The upside is the parts are made really clean which is crucial. The down side, is any highly polished
finishes tend to be made a bit dull. Dilutions are by weight not volume,
and my storage bottles hold 2.5 litres. For water, 2.5 litres weighs 2.5 kilograms. Two and a half kilos is 2500 grams and 2% of 2500g is 50g. With 50g of my final weight accounted for,
I’ll need 2450g of water. From this point on,
it’s gloves and glasses all the way. I start by weighing out the water. Then I weigh out the caustic soda. Remember: The reaction is exothermic. Always add the chemical, a little at a time, to the water. If the bottle starts to feel warm, leave it for a few minutes to cool before adding some more chemical. Next comes the anodising solution itself. The first time I had a go at anodising,
I tried sodium bisulphate on the grounds that it’s meant to be safer
and easier to obtain. There’s a link in the text to a site
where they’ve had good results with this, but I couldn’t get it to work. Bare in mind though,
I had no previous experience to back me up and I used the cheapest sodium bisulphate I could find which could have been icing sugar for all I know… Most American instructions begin with “Go to your local auto parts store
and get a quart of battery acid.” You’ll struggle with that in the UK. Battery electrolyte is available, but it’s not common. You certainly won’t get it in Halfords. Anyhow by chance, I came across a type of drain cleaner
that’s 91% sulphuric acid in a local DIY place. It was just on the shelf. Not even behind
the counter. No ID required. I was a bit surprised given that you can’t even buy pointy
things in the UK, until you’re 18. As before, I’m mixing by weight not volume. I want to end up with a total of 2500 grams
of solution. 15% of that needs to be acid,
which is 2500 x 0.15=375 grams. Now my drain cleaner is only 91% acid,
so I’ll need a bit more than 375g. In fact it’ll be 412g. I’ve already got 412g towards my
2500g of finished solution so I’ll need
2500 – 412=2088g
of distilled water. First I weigh out the distilled water. Then I weigh out the acid. It looks like I need to restock,
as I’m just shy on the 412 grams I calculated but a slightly weaker mix
shouldn’t have too much effect. To start with my water’s at room
temperature at about 18 degrees C. Remember: Add the acid to the water. And add it a bit at a time,
keeping an eye on the temperature. Here I’ve added about a third of the acid,
and got about a 10 degree rise. I added the rest of the acid gradually over
the next quarter of hour or so keeping an eye on the temperature. I was mainly trying to avoid
the bottle going soft with the heat,
and collapsing under it’s own weight. Interestingly,
it goes from purple to yellow when it’s diluted and it goes clear the first
time it’s used for anodising. I’ve every faith in the bottles that I use,
and I’ve never had one leak. But just in case, I keep the mixed
solutions inside extra tubs when they’re not being used and I store them on the bottom shelf. Seems like this way it would cause
least mess if one were to let go. The last solution to make up is the dye. There’s plenty of options for dye. Lots of people like ‘RIT liquid fabric dyes’ but I can’t get those locally, and online they’re close to the cost of metal dye, so I haven’t tried them. This type of Dylon is what all my local shops stock. I’ve tried a couple of colours with zero success. There’s a lot of stuff in the pouch.
Certainly more than just a few a grams of dye. It’s probably great for fabric, but it’s rubbish for metal. I’ve also tried some old fashioned Dylon
cold water dye that I picked up at a car boot sale. ebony black, emerald green and tangerine orange all worked to a greater or lesser degree. This a piece of scrap dyed with the black. This is the orange which has worn off quite a bit and this is the green, which didn’t work too well
because the panel wasn’t cleaned properly. I’ve found the cold water dyes don’t like
being stored for months on end. Over time little bits form in the solution
which spoils the result. A coffee filter will clean it up, but it’s a messy business, and I wouldn’t recommend it. If you’ve time to experiment there are places
reporting success with fountain pen ink ink jet printer ink,
and various other things. This will be my first time using
proper anodising dye. The instructions say 1 gram to a
litre should give good results. My dye tub holds 750ml
so I need three quarters of a gram of dye which is just a pinch. So that’s all the solutions ready to go. The next thing is the power supply. Small parts like mine don’t need anything very powerful. And this one will give 5 amps at 24 volts. For my first attempts I used it ‘as is’. But after doing some research I found out that a constant current
supply gives the best results so I built this ad-on unit. It’s just a Banggood switching regulator
module put in a box. It means I can set the target current and leave it to look after itself instead of having to manually fiddle
with it right the way through. The final bit of home made equipment
is this magnetic stirrer. It’s just a little motor an eBay speed control module and a nylon disc with two magnets glued into it. These are called ‘fleas’ and come from
China for not much money. I admit this is a bit overkill but it does helps to stop bubbles
sticking to the surfaces. I make the cathodes are made from thick aluminium foil cut from these party platter plate things. They last for a few goes, but are basically disposable. Lead is supposed to be a good choice for the cathodes but it’s surprisingly hard to get hold of. I use two or more large cathodes, depending
upon the shape of the part to try, within reason, to make all the paths between
the electrodes similar. My reasoning goes like this:
If I used a single ‘post’ type cathode, the nearest end to the part would initially see
all the current, and as the oxide layer was built up an area further
up the part might offer the lowest impedance and see some action.
But its anybody’s guess if the opposite end would anodise at all. In order to set the power supply I need to know the surface area of the part. I’ll just treat it as a rectangular bar and ignore the holes. That gives me two surfaces of 11.4 by 0.9 Two surfaces of 11.4 by 2.2 And two surfaces of 0.9 by 2.2 All told that’s about 74.64 square cm. This value is plugged into a 720 Rule Calculator. Entering the numbers I get 120 minutes, per mil of thickness, for a current of 0.48A I usually leave the amps per foot setting
at default value of 6. The electrical connection to the part is made with soft uncoated aluminium craft wire. Where possible I make two or more connections. The reason being: as the anodising progresses
the insulating oxide coating will build up all over the part.
If contact is broken the chances of reconnecting to that exact spot are zero.
The chances of getting a good contact elsewhere could be difficult if a
decent layer of oxide’s already built up. I fold the end big enough to jam it into a suitable hole. The connection needs to be good
mechanically as well as electrically, to minimise the chances
of the part falling off and having to fish around in the bottom
of the acid tank to get it back. The next bit is really important. The part must be spotless. Any greasy fingerprints will be
visible on the finished item. I start by cleaning thoroughly with brake cleaner until no visible dirt comes off the part. I tend to re-use gloves until they fall apart but for this bit, I use a clean
pair that won’t have any oil on them The part, and the aluminium connecting wire are given a final clean with MEK and then the wire is fitted firmly into the part with a hanging loop at one end. The first chemical bath is the
sodium hydroxide etch. It gets about 20 seconds or so in here, and
then a rinse in clean water. Here the power supply is short circuited,
and the maximum current is set to that calculated by the 720 rule. The two cathode plates are connected together,
and then to the power supply negative. Once the tank has been filled with the 15%
sulphuric acid solution, the part is hung inside on a wooden sick, something like
equidistant between the cathodes. The circuit is completed back to the power supply. After a few seconds you can see thousands of tiny bubbles forming in the tank. Each bubble creates a minute splash of acid when they reach the surface and burst. I’d strongly recommend lightly coving the
tank with a tissue or everything in the vicinity will start corroding. And that’s it for two hours. Just come back
and check nothings going wrong every so often. When the time’s up, the power is removed and
the part is thoroughly rinsed in water. Next comes the dying. This is optional, the
part can be just left self-colour if you just want to make it a bit more
corrosion or scratch resistant. Just agitate the part in the dye until it
reaches the colour that you want. This is my first go with real metal dye and I have to admit it miles better
than anything else I’ve used. The colour is deeper, and is fully absorbed. Other dyes I’ve tried look ok,
until they’re rinsed, when a lot of the intensity just washes off. The final stage is to seal the part. I’m simmering it in boiling water for about 40 minutes. Once cooled the connecting wire can be removed
and the job’s finished. This is one of my better attempts, though
it’s still not perfect. I’ve got a bit of a tide mark on one side.
I’m not sure what caused this. Perhaps drying the part between
baths would help? To finish up, here’s the part fitted in the
puller that I was making. And that’s it. Thanks for watching!


  1. Post

    I live in Thailand, they have road side stands here that sell every conceivable kind and type of knife, hatchet, Machete's of every size…Etc. I'm sure i can easily get barrels of shark water here as well…i may try this Anodizing after casting my own parts. Nice Video btw.

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    Mike Bee

    Great job, very easy to follow & good results, I'm now a subscriber. Side note: I can't believe it's so difficult to get simple chemicals in the UK, I hope the USA doesn't follow suit however something tells me that they will.. Thanks for posting this video.

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    Nagy Andras

    maybe you get better results if you connect 2 equal wires to the aluminium foils, then connect those wires at a single point to the powersupply. there is a verry small difference between this, and connecting them up the way you did. not sure if it helps a lot, but supposedly thatway you got equal resistance in path.

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    Were can i find the calculator you are using in the video outside the machinist forum. they ask more data than a forum needs to ask to be a part of it.

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    Josiah McGlothin

    I feel like I'm watching a BBC Presentation, the quality of your audio is great and you've got the voice of a presenter, love it!

    Oh the content is great too, hahah. 🙂

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    I drifted here after looking for something to watch, excellent and comprehensive, top video, i remember vaguely using a nitric acid bath before the anodising, I just cant remember what the other wash was.

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    Warthog 71

    Excellent presentation. I love the mathematical conversions. I’ll post my attempted results on my channel. Thank you!

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    ROB G

    When sealing the aluminium peace after dyeing it your better off using sealing dyes at 60 degrees Fahrenheit for 20 to 40 minutes

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    ROB G

    I used to do anodising as a job for seven years you have most of this on point and once you have cleaned the item don’t put it down just rig it up and place in the tank or container to be anodised so the will be no more contamination to the job anodise item for required time then rinse though two distilled water then put into a hot 60 degrees water with sealing salts for aluminium then the item will come out perfect 👌

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    Terry Mooney

    Sodium acetate added to the boiling water seal will aid in stabilizing the dye color over time. It will also leave a whitish film on the part that wipes off.

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    Alex Barnett

    I'm interested to know if you could use blood to dye an anodized part with. I'm not going to try it but I'm just curious. I feel like it would probably work. Any thoughts?

  21. Post

    that the sulfuric acid becomes colorless isn't difficult to explain, Sulfuric acid is an extremely strong oxidizing agent, this means that concentrated sulfuric acid will oxidize all organic molecules down to carbon dioxide, especially when heated, in chemical or biological laboratories a mixture is used called Caro's acid or Peroxymonosulfuric acid, it consists of concentrated sulfuric acid and 35% hydrogen peroxide solution, it is used to clean glassware, If, for example, some cotton is thrown in, it will be completely oxidised up to CO2 and the remaining solution is then clear again. A warning to all those who want to imitate this acid now, it's highly dangerous, if you get some of it on your skin, that gives terrible burns, worse than sulfuric acid alone, so hands off, if you don't know exactly what you're doing!!!!

    Oh, before I forget, a great tutorial btw. 👍👍👍

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    the moose

    I enjoyed your video. I have watched several and I think yours is more informative than some others. I will try your technique since it looked like you had some great results. I will try drying my parts before adding to color. Thank you from California. Now if I can just get the chemicals. Therein lies the rub!

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    Steven L

    Great video! Do you have any more information on the homemade stirrer and the constant current module? Thanks.

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    The uk is ridiculous, treats its people like children! No acid, pointy things, lead???? Ridiculous!!!

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    Magna Bumi Putra

    The magnet rotary you had is causing the difference in colour.

    The acid solution flows only in one direction and corroding more of one part than the other, unless you can find the eye of the whirlpool by actually placing the object in 0 median but you will require an even bucket as well.

    You don't need those magnet rotataries.

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    Absolutely the greatest description of water to acid/acid to water in the history of the internet!  Bravo sir! Bravo!

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    ivan schafeldt

    have you made any attempt to get the certificate required to buy chems since the 2015 act?
    i want to do silver plating but all formula's require nitric and im not sure if the process is a ballache or not, im not a big fan of dealing with officialdom

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    Dav Mar

    NIce! One suggestion, make yourself a vapor degreaser. That is by far the best way to thoroughly clean every surface, including holes, of any metal part.

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    Sylvain Girard

    Awesome explanation! Just seems like a lot of work with funky chemicals… Not really worth it, imo

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    Simple way around the law with sulphuric acid, you can concentrate battery acid by boiling it or do a distillation but you need good equipment to do a distillation or make it your self making acids is rather easy even Nitric acid, screw the law lol dunno why they ban such a useful thing, are government don't care about stuff that really need fixing they resort to ban stuff and not trying to sort the actual root of the problem like for example banning a certain type of knife that was used in a crime but that's stupid people will use a different knife instead, for acid attacks then you can use boiling sugar and bleach instead or oil or boiling lye or go full mental and use a knife or something there is always a loophole or workaround, like when they made guns harder to own and banned pistols knife crime went up way higher if someone wants to kill or screw someone up badly they will somehow.

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    Kassie Myburgh

    Loved this video, awesome quality and detail. Perfect help for DIYers. Thank you for sharing.

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    Sayit AsItIs

    I love these videos about fiddly little projects that I know I am never going to do.. This was about 9 on the fiddly scale and a 10 on 'Not Using It' scale.

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    Joe Bledsoe

    Dishwasher soap or perhaps its called detergent is sodium hydroxide, its also called lye or lye soap. Don't know the qty or strength.

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    Joe Bledsoe

    Sulphuric acid is in car batteries bit I don't know the strength only that one measures the specific gravity to check the status of the batteries charge.

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    You're so lucky to have a government that passes laws to protect you. I bought a sharp pointy object on day and no one asked for my ID. A few days later, I nicked my finger with it. It took days to heal. That wouldn't have happened if they had asked me for an ID.

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    09:50 Lead can be got from your local church 🙂
    I don't know if you can still get lead flashing my the meter but you could try your local Builders Merchant,

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    garrett halsell

    Very Accurate representation of how Anodizing is done! I am an anodize technician and for the most part, you are spot on! Since most of the chemicals are variable depending on who you ask, the only kind of tip I could give you for future reference is that heating your dye will help immensely, then wash with cold water after that. Also if you want a thicker and more durable coating on your part, take the temperature of your anodizing tank down to around -1C Degrees. That will make it more wear and corrosion-resistant.

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    Curtis Newton

    you need 412g from 2500g, so you add 2088g of water ????
    I really dont understand that part, just take out 412g and that's it

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    Ian Watson

    I use that drain cleaner as my daughter's long hair often bungs the drain pipe up in the bath, have to put it down and wait 5 minutes then turn on the cold tap cos leaving it longer it eats the pipes its that potent lol The smell of burning hair and skin and the smoke out the plughole is really horrible but it does work extremely well and I was surprised at no checks at my local Sydenhams when I buy it O.o

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    Buhda Punk

    If I understood distilled water 101, it is somewhat free from any dissolved solids or contaminants giving the acid less of a media to react too. I am sure you could do something with blood and sharks? less blood, less reactive shark maybe. Thanks for the vid its one of the better explanation. Be careful on the narrating though, to many state-side info-mercial product salesmen with fake British accents giving a bad wrap to gentlemen like yourself. BTW I used colored leather dye as wood stain "gold and yellow". I used piece of scrap aluminum to stir the mixture. It stained the aluminum a nice amber almost titanium color.

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    Buhda Punk

    I going to put a guess out there but those little bubbles at 13:40 or so are hydrogen. Hydrogen Sulfide spray great skin remover

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    Paul Chamberlaine

    Brilliant video, informative, sufficiently detailed with reinforcement where appropriate and narrated clearly at an easily absorbed pace with no distracting musak. Very enjoyable. Thank you very much.

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    Brian Park

    There is another "secret chemical" you need to get the best dye retention. Nickel acetate. You only need 1 gram per liter in the boiling solution. If you can't buy it, you can make it a from a piece of nickel metal dipped in vinegar and hydrogen peroxide. (Alternatively, if you can get nickel carbonate, mix this this with vinegar until just dissolved. If you can get other soluble nickel salt, add sodium carbonate washing soda or sodium bicarbonate baking soda to precipitate nickel carbonate.) Add the peroxide a little at a time over several days. Solution should turn dark green. Evaporate the solution (don't use high heat) until green crystals form. Filter these off, and rinse with small shot of cold water to remove vinegar. Dissolve this in post-boiling solution. This causes the pores in the anodizing to swell shut and seal in the dye.

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    Max Brandt

    I enjoy anodizing, when I have parts to actually finish! The nautical industry is a fickle one even if the US economy is doing very well.

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    Max Brandt

    The key thing when anodizing is super clean parts, cathodes on both sides of the aluminum part, boiling hot dye to color the metal once the part is anodized and boiling hot sealer to finish off. Talk to the people at Caswell Plating, I think they ship internationally.

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    Perma Grin

    That’s a bitchin vid. Well put together and explained. I just bought a mill and lathe and have so much to learn. Watching this is the ‘finishing touch’ to projects.

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    Tony Nameless

    Dont feel bad man, in the US you are not allowed to buy alcohol until 21 yet you are allowed to have sex with a 16 years old with absolutely no age game limit.
    Which one is worse, alcohol or sex ?
    Government is full of idiots passing laws like that.

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    Archie Bunker

    I came here looking for info on anodizing aluminum parts. I'm leaving here at peace with spending the money on professional anodizing.

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    hold on a minute…. if the acid is 91%, and you need 375g, then you should add 412g of the acid but only count it as 375g as for your final weight??? unless that extra 37g is only pure water, it shouldnt count towards the mixture total as it is an inert ingredient, no?

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