# Proof of concept - Etching aluminium with masking



## BradG (Oct 18, 2012)

Now im getting excited about this.

I have been wanting to find a way of masking out aluminium and etching the remainder, without effecting the mask, or under cutting it.

Generally speaking, caustic soda is used for etching aluminium, but its far too aggressive for a vinyl mask working its way underneith and causing faint outlines and wobbly edges.. not good.

I have been experimenting with others, and the best i have found is with Ferric Chloride. It seems to have an exothermic reaction to aluminium, and the deepness of this etch was obtained in as little as 2 minutes. Quite impressive. I am yet to get a pair of digital calipers on it, but a guesstimate is of around 0.25mm which feels great under the finger as embossed lettering.

The catch here, si that it is no way as clean as it is when using sodium hydroxide as you can see by the amount of smut left on the piece where it has etched. One suspicion i have is that the Ferric is laiden with copper from stripping PCB's which could be adding to the contamination of the metal surface. I cant wait to get home tonight to try it with clean ferric to see if it improves the finish.

If not, well im not going to lose sleep over it. It just means i will then continue to find the best way of desmutting the piece, as how it stands - its not clean enough to be anodised.

I would imagine a blend of sulphuric and nitric acid will yield a good desmut as it wont attack the aluminium. I may even experiment with ultrasonic cleaning, though i am concerned that the formation of bubbles may have an effect on the edges of the mask, which i may intend to leave on trhought the entire process I have in mind. Perhaps running one at 130kHz may produce large enough bubbles not to have a detrimental effect, though i can see that being another experiment thread all in itself.

So what am i thinking...

The text BAD is just from a set of vinyl i had laying around. I intend on masking out an image, and etching the underturned body of a gent pen down to its correct diameter. I am working on a calculation of etch time at a specific concentration of ferric, to yield the correct diameter, though i can see this behaving completely different when i switch to fresh ferric tonight.

Once this is etched, i will then have a slightly raised graphic on the body of the pen, in nice shiny fresh aluminium. The mask will be left on, the piece cleaned, anodised, and dyed, which in effect creates the background colour.

After sealing, the mask is removed exposing the bare aluminium.

I then plan on zincating the exposed aluminium, then copper plating, then nickel plating, then either chrome plating or gold plating - depending on the look im going for.

Still a few more steps to perfect, but wow i can see these pens popping in photo's


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## neubee (Oct 18, 2012)

It sounds like a good project; beyond my level of comprehension though.


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## trapper (Oct 18, 2012)

Hi brad seems an acceptable result to me I might try and incorporate this into a current project I'm working on. whats your thoughts on cleaning up the smut....... i guess a repolish and plating or annodizing ?


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## BradG (Oct 18, 2012)

As mentioned most probably a nitric based desmut. Plating aluminium isn't straight forward. Anodising is good, depending on your project


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## BRobbins629 (Oct 18, 2012)

Another sloution that will etch aluminum is a combination of copper sulfate (10g) hydrochloric acid (80g) and water dilute to 1000 ml.  It will work quickly as well and at room temperature. Never tried it with a mask, but if you want to experiment, just be careful. You can adjust the reaction time by adjusting the concentration of HCl.

CAUTION: This should only be used by those comfortable handling potentially dangerous chemicals and with proper safety precautions.


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## BradG (Oct 18, 2012)

Thanks Bruce, if the smut proves problematic il try hydrochloric.


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