# Anodising at home.



## th62 (Sep 11, 2021)

[original post, restored by moderator]
    I bought 5 litres of acid and cobbled this anodising bath together, easy as.

    10litre plastic bucket filled with diluted acid, two aluminium cathodes, wired together, a Projecta battery charger/power supply and a bit of aluminium wire. I'll be updating the settup with titanium wire , lead cathodes and an ammeter as soon as they arrive. But it does a good job as it is.

    First shot is the first piece I anodisied. This piece was mirror finished before being anodised. As you can see, it dulled the shine, but did give a nice finish. Second and third shots are of my second test piece, half the strip was polished, other half was brush finished, came out much the same both ends.

    Final piece was the cable splitter I made. I assembled the the splitter with O rings on both end caps and inserted rubber bungs in the three holes before dunking it in the bath. This was necessary as the threads are a very neat fit, if anodised they wouldn't fit together. Also, I didn't want the bore anodised as this would effect the fit of the brass slide. Came out with a nice grey finish.

    Happy with the results. Another tool to add to my collection.


----------



## graham-xrf (Sep 13, 2021)

Nice finishes. That comes from meticulous cleaning!

Foe me, the sulfuric acid supply has become awkward, apparently because of people who would attack others with it. It makes no sense. I don'y thing any sales restriction measure would do anything to make a difference except inconvenience users. Now, in UK, you can't even buy battery acid! It only moves in bulk to licenced registered manufacturers, I think with every drop recorded. You can buy reagent acid in small quantities at crazy prices.

I scored some on eBay about 2 years ago, and I have it stored, and I use it sparingly.


----------



## RJSakowski (Sep 13, 2021)

Fifteen years ago, I did some anodizing of parts for a project that I was working on.  I built a 25 amp constant current power supply with a digital volt/ammeter. I used aluminum grounding wire from a tv antenna for my electrical connections and threaded some aluminum rod for use where I had threaded holes in the workpiece.  My cathode was a sheet of aluminum from a distribution transformer. My results were satisfactory for clear anodizing but I was unsuccessful when I tried dyed anodizing.


----------



## RJSakowski (Sep 13, 2021)

In the states, we can still buy battery acid at auto supply stores.  $10 for a quart.  If I recall correctly, battery acid is 25% sulfuric acid and is diluted  to around 10 - 15% for anodizing.


----------



## addertooth (Sep 13, 2021)

... and don't forget the high temperature steam for sealing it afterwards... that is part of the process too, for a lasting anodized coating.


----------



## th62 (Sep 15, 2021)

Nothing to see here.


----------



## th62 (Sep 15, 2021)

Ditto.


----------



## addertooth (Sep 15, 2021)

th62 said:


> Actually it's boiling and that's for sealing in the dye.  Not required unless you are dying the anodising.


Closing the pores makes even a clear anodized coating less susceptible to chemical attack.   It is vital for sealing in dyes, but it also has use for clear.  They "big boys" use steam, as it allows them to perform this function on larger batches with greater ease, but yes, boiling water works too.


----------



## RJSakowski (Sep 15, 2021)

th62 said:


> Battery acid is 35% sulphuric acid.  For anodising it's further diluted down to around 19%.  Both battery acid and sulphuric acid are difficult to find in Oz too.  Motor accessory outlets and battery outlets are not permitted to sell it, the only place you can buy it are from chemical outlets.


You have to state whether the concentration is weight/weight or volume to volume.  When I worked in an analytical chem lab back in the seventies, we used a dilution of 1 part sulfuric acid to three parts water which is a 25% v/v. solution.  Sulfuric acid has a sp.gr. of 1.83 so this would be a 38% w/w solution.  I noted at the time that this was very close to the concentration of battery acid.  Thinking about it, maybe we used that concentration because I worked for a battery company?

A 19% w/w concentration would be an 11.4% v/v concentration.  It is simpler and safer to dilute acid by volume rather than weight.    I dilute battery acid 1 part acid to 1 part water by volume for anodizing.


----------



## hman (Sep 15, 2021)

I recall hearing/reading about using sodium bisulfate instead of sulfuric acid for anodizing.  Here are a few links I found with a quick Google search:





						Anodizing aluminum
					






					sdiy.info
				











						Anodizing and dyeing aluminum without battery acid...
					

There is now an updated video on YouTube here . I did not show the dyeing step and it should be mentioned that after being in the dye, the anodized piece should be placed in boiling water to seal in...



					www.observationsblog.com


----------



## mattthemuppet2 (Sep 15, 2021)

I use sodium bisulphate and it works just fine. A nice thick oxide layer will give the piece a faint gold tint. Cleanliness is key (scrub with dawn, then acetone, then isopropanol, then do a water break test) and good dyes are a must.


----------



## th62 (Sep 16, 2021)

RJSakowski said:


> You have to state whether the concentration is weight/weight or volume to volume.  When I worked in an analytical chem lab back in the seventies, we used a dilution of 1 part sulfuric acid to three parts water which is a 25% v/v. solution.  Sulfuric acid has a sp.gr. of 1.83 so this would be a 38% w/w solution.  I noted at the time that this was very close to the concentration of battery acid.  Thinking about it, maybe we used that concentration because I worked for a battery company?
> 
> A 19% w/w concentration would be an 11.4% v/v concentration.  It is simpler and safer to dilute acid by volume rather than weight.    I dilute battery acid 1 part acid to 1 part water by volume for anodizing.


Ditto.


----------



## RJSakowski (Sep 16, 2021)

th62 said:


> You can buy sulphuric acid, or you can buy battery acid.  I stated, very clearly, I used battery acid.  If you buy battery acid it is clearly labelled on the container it is 35 percent sulphuric acid.  I don't know what lab you worked in, but dilution rates are measured by weight, not volume.  However, the dilution rate is not super critical.


I have a degree in chemistry and my first professional job was as an analytical chemist for a national battery company.  My 43rd ed. of the CRC Handbook of Chemistry and Physics, pp. 1664, has a page devoted to dilution of acid by volume for sulfuric, hydrochloric and nitric acids.

Diluted sulfuric acid solution can be purchased by either w/w or v/v.  Fisher Scientific, arguably the largest chemical supplier in the US, sells in both forms.  Here is one example. https://www.fishersci.com/shop/prod...on-for-phosphorus-spectrum/18614261#?keyword=

Acids are often diluted v/v because of the relative danger involved with weighing out concentrated acids. If the dilution method is not specified, w/w is implied. For precision work, we always used moles/l. as there is some additional ambiguity as to whether the method used was based on the volume of reagent to the volume of water as in the Fisher example above or the volume of reagent to the final total volume since for most chemicals, the the volumes aren't additive.

As to my original post, actually, we are saying essentially the same thing. My 1:3, 25% v/v solution is 37.89% by wt and diluting that 1:1 v/v is 22.8021.12% by wt.  This is in the ball park for anodizing.  As you stated, the dilution rate is not super critical.

Edit:  I used the wrong sp.gr. in calculating the final concentration. in the above paragraph.  The 21.12%  by wt. value is the correct concentration for the anodizing solution that I used.


----------



## RJSakowski (Sep 18, 2021)

th62 said:


> Well, if you have a degree in chemistry you should know that acid and water do not weigh the same, that is why, dilution rates are measured by weight not volume.



I am fully aware that there is difference in density of different liquids.  I am also proficient in all methods of dilution of liquids, having done so for almost sixty years.

Dilution of liquids by volume is common.  Antifreeze, fuel for two cycle engines, machining coolant are all done by volume.  Biochemists do serial dilutions by volume to make up their standard series. Most agricultural chemicals are diluted by volume.

As to dilution of acids, here is a page from "An Introduction to Semimicro Qualitative Analysis", 1sr ed. by c.H. Sorum.  This text has been a standard for collegiate chemistry courses for over 70 years.  All the acids and the liquid base, ammonium hydroxide, are diluted by volume.


----------



## mattthemuppet2 (Sep 18, 2021)

p!$$ing matches aren't super helpful to be honest, it would be much more useful to focus on anything that might help the OP or anyone else who's reading. That is if the OP wants any help or if this was more of a "look what I did" post?


----------



## mattthemuppet2 (Sep 21, 2021)

I think you're arguing with yourself mate, everyone else has left the room.

[moderator]:  to avoid confusion, the improper and slightly abusive posts by th62 have been deleted as obstructive to the thread.


----------



## Dabbler (Sep 22, 2021)

The OP, Th62 posted this at the top of the thread, edited:

This post was meant to show anybody thinking of doing some anodising how easy the process is.  I am by no means an expert, however, my technique follows that of 'anodising' professionals.  I want nothing more to do with it.

I have locked this thread as it appears that it has caused hard feelings.  Anyone wanting to comment or for more information, PM @Dabbler


----------

