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electrolyte for etching aluminum

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ZakWolf

Tue Jul 19 2011, 08:25AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
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Posts: 608

I read that making a black etch mark on aluminum requires DC and a special electrolyte, I cant seem to find anything on the intertubes and was wondering if any one knew of such electrolyte.

Ash Small

Tue Jul 19 2011, 09:45AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I've not read this fully, but apparently you don't even need electrolysis, just HCl and H2O2

There are a few ideas here:

,or.r_gc.r_pw.&fp=1cf90f5820d223e3&biw=1366&bih=65 3

I don't have any personal experience of this myself, but I'm interested in giving it a try.

ZakWolf

Tue Jul 19 2011, 10:04AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
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Posts: 608

Yeah i saw that instructable but i just dont want to deal with any acids, i have all the electrical equipment i just need to know what metal an electrolyte to use, hopefully something common and maybe even house hold.

Pinky's Brain

Tue Jul 19 2011, 01:54PM

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You can get anodization kits for aluminium, these form a porous aluminium oxide layer which can be dyed.

klugesmith

Tue Jul 19 2011, 04:48PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

There's nothing critical in electrolytic marking. Try salt water to start with. Ought to make a decent, permanent mark on aluminum in a couple seconds. (If the Al surface is already anodized, thus nonconductive, then you're SOL.)

In a typical commercial system, you:

1. Make a stencil of desired mark. They sell special coated paper like old mimeograph stencil stock, that becomes porous when typewritten on. Now go find a typewriter.

2. Stick the stencil on the workpiece.
3. Choose one of their proprietary electrolytes, depending on your metal.
4. Use electrolyte to dampen a metal-backed felt pad, which is the tool.
5. Connect their DC power supply to the workpiece and the tool.
6. Apply tool to stencil for a while (10 seconds max).

I still have some high-speed-steel endmills, on which I etched my name at a summer machine-shop job 35 years ago. The marks look good as new.

Conundrum

Tue Jul 19 2011, 06:04PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Interesting, some EL panel manufacturers use this in their "ICEbrite" technology to increase the contrast ratio.

-A

ZakWolf

Tue Jul 19 2011, 08:44PM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

thanks, I will try the salt water but what other metal do i need, will steel work, i thought different metals plated different things. To make a black mark I guess i need DC for aluminum, but i will try both.

klugesmith

Wed Jul 20 2011, 03:03AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

It doesn't much matter what the tool backing plate is made of.
The workpiece is positive and the tool backing plate is negative.
You are _removing_ metal from the workpiece, not plating metal onto it from the electrolyte.
The mark is black because of microscopic roughness or a secondary chemical reaction.
See:

[edit] the top two comments on the you-tube video are stupid.
They claim that the salesman demonstrates the process on one side of a knife,
then cuts to a close-up of the result on the _other_ side of the knife.
To my eye, it's just a different view of the same side of the knife.

Reminds me of this video of a narrowly-tuned tethercar reaching 200 real (not scale) MPH.
Dummies are always posting comments calling it fake, with various stupid arguments.

[re-edit] On closer inspection, the knife-marking demo does switch sides between
application of the tool and close-up off result.

ZakWolf

Wed Jul 20 2011, 03:26AM

Registered Member #3114 Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608

so i will try with some salt water, AC or DC what voltage?

Ash Small

Wed Jul 20 2011, 01:25PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

SublimeVolts wrote ...

so i will try with some salt water, AC or DC what voltage?

DC. Workpiece is positive (anode).

The critical factor is current/area (amps per square metre, or in this case per square millimetre)

I'd start by making a saturated solution of salt water by boiling the water with excess salt, You may find that temperature also has an effect on rate of etching, current required, etc.

Start with a low voltage. if nothing happens, increase the voltage. (or try limiting the current with a resistor, light bulb, or whatever, it's the current that is the critical factor, not the voltage)

Distilled or de-ionized water may be better than tap water, but I don't expect it will make a lot of difference.

(I might try this myself)

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