Stripping Anodise With Hydroxide

Just a quick note for anybody not familiar with the use of Sodium Hydroxide to strip anodise.(My apologies to those that use this stuff frequently)

Sodium Hydroxide aka Caustic Soda, causes an exothermic reaction when mixed with water, a few don't do's.

DON'T pour water into the Hydroxide pearls / crystals, always add crystals / pearls to the water.

DON'T add HOT water to hydroxide or hydroxide to hot water (it changes the reaction speed and can easily result in a steam explosion throwing hot hydroxide solution all over the place, you think this stuff is nasty cold, you want to see what it does when it's hot) A hydroxide reaction can easily reach 200 degrees, at that temperature water flash boils into steam and really can chuck this stuff a long way.

Concentrated Sodium Hydroxide has a burn factor of 9, Concentrated Nitric Acid has a burn factor of 6, Concentrated Sulphuric Acid has a burn factor of 5.

If the solution or crystals get on your skin or in your eyes, water...LOTS of water and keep the area irrigated for at least 20 minutes, then in the case of eyes go to the A&E department / Emergency Room of your local hospital and tell them what the contaminant is. Don't just give it a quick rinse off or you may find when your watching TV later that evening you get a burning sensation starting all over again.

1:2 Crystals / Water by volume will make a good strong mix that will strip both Caustic and Hard anodise in a matter of minutes.

Water isn't great at removing the solution from those nice expensive hosts in all the tight corners, when you have finished stripping remove the host from the solution, drop it into a container of vegetable or cooking oil. Agitate to make sure the oil has gotten into every tiny area of the host and leave overnight.
In the morning you will find that any remaining hydroxide has turned into a rather efficient soap and can be washed away with warm water. Same goes for the used solution, simply add cooking oil at a 3/1 Oil/Solution (by volume) and that evil gunk will all turn into soap overnight.

The usual rubber gloves used for dishwashing etc are no good for use with Caustic Soda, it will damage the structure of the gloves to a point your fingers will suddenly poke through them (not nice) so always use chemical rated gloves.

That's about it

My sincere apologies to the vast majority who already know this, I just wanted to be sure that no new members get badly burned when stripping anodise with Hydroxide.

best wishes

Dave

Great tutorial. Not something I was familiar with. (I failed chem at high school ) Thanks for the info.

Thanks spooky! Good info!

Yeah good information.

Very good info... but for the ones that have never done that before, do you just put the host in that solution or do you wipe it with a towel? A good video tutorial would be great. I usually use a sandblaster to take the anodizing away but this seems even more efficient.

Hi Guys,

Thanks for the kind words

Just dip the host into the solution (remember the gloves) 3 to 5 minutes or so will remove most of the anodise but keep checking to make sure you don't burn the base metal. It can be brushed on but to be honest I don't like having my hands or face anywhere near this stuff.

To check that all the anodise is gone use a simple bulb / led and a battery, anodise (aluminium dyhydroxide) is a very good insulator so no current means there is still some left behind.

I'll get a video done as soon as I can of the "how to" as well as a vid of a flash steam explosion I made a while ago (just to illustrate how far this stuff can go when hot)

If anybody wants to know how to set up a home anodiser I can post a video of that too? (it's actually really cheap to do with a full set up costing under £100) It's also not that hard to anodise titanium, the colours are controlled by voltage rather than a dye additive but the solution is a lot safer, it's basic coca-cola (weak phosphoric acid)

In the UK B&Q sell caustic soda at around £5 a kilo for crystals in the plumbing section.

best wishes

Dave

Some solutions are available which remove the dangerous measuring and mixing step. Would drain opener be safer in that regard, for someone who wants to only strip anodizing from a single piece?

^^^ In the solution. You can also just stick it in under a tap once you have removed it from the solution to remove the excess hydroxide. If it still feels slippery or soapy when you're done you havent removed it all. Just rince it some more and if you really have to get into the threads you can use an old tooth brush...just remember to wear some safety googles when working with strong alkaline or acid solutions and esp with a brush!

Nitrile or PVC will protect your hands and these are cheap in the hardware store. If you do happen to damage them and get some of the solution on your hands dont panic wash it off immediately (good idea to stand next to a sink whilst working ) Rince for 10 -15 mins under running water and just make sure your hands dont feel soapy. I have spilt a few very strong acids and bases on my hands during work/ study in the past and it isnt an issue if you are quick ie within a 30 seconds or so you wont even feel it. Yes you must be very careful, but again dont panic! :beer:

The saponification idea is really good, you could even choose different oils or fats to make a different scented soap to wash off! +1 for the idea and great write up! :beer:

@ Banashan Drain opener if in the form of powder contains aluminium powder to accelerate the reaction. If you could buy a solution of 1 - 2 Molar sodium hydroxide that would work and I think you can get these solutions as drain cleaner in the US. Other drain cleaners that I know of in the UK use H2SO4 (sulphuric acid). So always good to check the label :beer:

Indeed as Grainde said, a lot of drain cleaners are Acid not Alkaline.

Sulphuric will remove anodise but it's also going to eat the host base material quite quickly (anodising is done with Sulphuric)

best wishes

Dave

Gotcha, so make sure the drain opener liquid says sodium hydroxide or lye or base, but nothing that mentions sulfuric, acidic, sulfuric acid or H2SO4?

Thanks for the clarification. I wouldn't have liked using the wrong kind of solution and ending up with a bucket of dissolved flashlight :crackup:

edit: also, thanks for the tip about nitrile gloves. I'm assuming typical box-o-latex-gloves isn't for dealing with caustic chemicals the way nitrile is?

Pretty much I don't know about the US or overseas but here (UK) the label has to show what chemicals stuff like draino contains. Usually the strongest active ingredient is listed, Caustic Soda , Sodium Hydroxide are the main ones to look for.
Splash stripping can be good, paint solution where you want the anodise removed then wash and polish for a tiger stripe effect

best wishes

Dave

BShanahan14rulz said:

Some solutions are available which remove the dangerous measuring and mixing step. Would drain opener be safer in that regard, for someone who wants to only strip anodizing from a single piece?

Click to expand...

I just used the jel type to remove the clear ano off Kryton in less than 5 minutes. Clean up with soap and water. Then just quick hand polish and she looks great.

I first used Caustic Soda in the early 1980's to strip the unpopular coloured or cheap to buy anodised parts & then polish them up to a mirror finish to either use on my BMX bike's or re- sell the Shiny polished parts parts to the rich , stupid kids who were funded by their parents to support the full time habit I acquired as a teenager.
Over the years I continued to use Caustic Soda to help make Aluminium Alloy components look like they were Chrome plated to help support the other expensive habits I picked up like high performance Race & Street Cars...

Spooky has covered most of the tips for new users , I might throw in a few other tips I have picked up over the years.

Always remember you are working with Fire's , Older Meaner & Unforgiving Big Brother.

Eye protection is _mandatory_ , so find something comfortable that offers plenty of coverage to be wearing all the time you have an active caustic solution around you.

Don't wear any of your favourite/expensive clothing or Jewellery when working , something will eventually get dropped into you Caustic Bath & those little droplets will burn whatever they land on.

If you are doing a large run , have 2 extra buckets of water , one to rinse all the caustic solution off into & another clean bucket of water to store & examine freshly stripped pieces under water to see if they need to be put through a strip & wash again , the less time freshly stripped Aluminium spends rapidly oxidising in the air the better , you don't ever want to be working a hurry or a confined area with a Caustic Soda solution.

Have some sort of skin friendly acid around to take care of burns or spills.
Over the years I began to keep a squirt bottle full of White Vinegar to keep close by when working with any Caustic solutions. Acetic Acid in natural or concentrated form will quickly neutralize a Caustic mixture down to a friendly & neutral mixture with a Ph value of 7.
The Vinegar is extremely handy to have if things go South or you need to stop work fast.
A freshly cut Lemon , Lime or Orange also comes in handy to use to wipe yourself or something that has been splashed with a Caustic solution.

Work outside if possible , if you have to work inside work set up a roomy work area in a well ventilated room with a fan running to blow the fumes out. The fumes that come off any Caustic solution will damage , burn or rip your lungs out , pending on it's strength & length of time you are exposed to them.

Polishing a stripped piece Aluminium Alloy to a mirror finish is an Art of it's own.


If you want to remove surface rust that has built up on something that is Chrome Plated & bring back it's original Bling back you might want to find some Oxalic acid preferably in powder form.
As long as the rust has't pitted _all_ they way thru the Chrome plating to the base metal , it can & will perform miracles.

Your on your own if a Stainless Steel piece has "failed the challenge"


JB

Jet Black said:

Have some sort of skin friendly acid around to take care of burns or spills.
Over the years I began to keep a squirt bottle full of White Vinegar to keep close by when working with any Caustic solutions. Acetic Acid in natural or concentrated form will quickly neutralize a Caustic mixture down to a friendly & neutral mixture with a Ph value of 7.
The Vinegar is extremely handy to have if things go South or you need to stop work fast.
A freshly cut Lemon , Lime or Orange also comes in handy to use to wipe yourself or something that has been splashed with a Caustic solution.

Click to expand...

Some great info, but its not recommended to use acids to neutralise bases spilt on the skin and likewise the other way around. The citric acid contained in oranges shouldn't be too, bad but I wouldn't consider using vinegar (also comes in many different concentrations from very dilute 1-2% to glacial - people may not realise this...). Aside from the rather exothermic nature of acid base reactions further injuring tissue, you'll probably shoot through the roof in the process.

The best option for skin, and especially damaged skin, is rinse with copious amounts of water for at least 15 mins. :beer:

i have a groove that needs the anodizing removed from the threads etc. i'm going to try applying an NaOh solution with a q-tip or something. will i be able to see the solution doing it's work?