Electrolytic etching

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BradG

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Electrolytic Etching is something I've wanted to do for a while, as it replaces the messy use of Ferric Chloride which stains everything it touches. I'm also not overly keen on the fumes it can put out.

Another benefit is that Electrolytic Etching is much slower compared to exothermic reactions, giving you greater control over the process.

Much nicer handling salt water oppose to other far more aggressive corrosives. alot easier to clean up if you spill.


The system consists of a small tank of salt water, with a sacrificial stainless steel cathode, connected to the negative of the power supply. The part you are etching becomes the anode, being connected to the positive of the power supply.

The catch?.... yes there is one. The power supply required for this needs to be quite powerful. Currently, my variable power supply can be set between 0-70V 3A. For this process, I should be using at least 10A, so I am severely under current. The target goal would be 1 volt, and you would increase your current until you can achieve this. To my understanding higher voltages and insufficient current will cause pitting, as can be seen on the big open areas on the etch below. I sanded the surface of the etch so you can see just how mottled it is.

On a plus side though, look at the areas in between the cogs and the areas surrounded by masked metal. they are silky smooth! really impressed with the finish here.

The depth is great and would hold a variety of background fillers & paints well. This etch was for 1 hour 10 minutes, and I suspect this will be around 30-40 minutes once I've saved up enough to buy the bigger power supply.

I just noticed in the pictures, the etch is deeper at one end, which will be caused by the cathodes laying on the bottom of the tank oppose to running parallel down the sides.

Il keep working on this one to see how I can tweak the process, and il put a how to guide together once I've cracked it.

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H2O

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Just curious...
Why use the chemical method as opposed to using a mill?
With a mill, there aren't the chemical hazards, and the process could be done a little faster.
 

BradG

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you would have to use a CNC mill. out of the price range of most here.

Chemicals are fine when handled and used correctly. same as a mill. disrespect it, and it will take your finger.

Also doing it on a mill really wouldn't be faster unless you're talking making batches.
 

magier412

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I really like the look of that etching...deep and clear...and the pitting gives it an industrial look in my view. Very cool!
 

BRobbins629

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Every time I tried etching my biggest problem was the mask. Tried many things but never got as crisp edges. You seem to have conquered that. Anxiously awaiting your procedure. Most experiments were on copper.
 

BradG

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Bruce, the secret to the mask is using a kettle. follow this step by step and you'l have crisp edges

1) Thoroughly wash the part, I like to use caustic detergent nowadays.
2) once completely dry (don't touch to check.. you will leave oil on it), apply sign writing vinyl stickers making sure to take your time and apply evenly. Get in touch if you need some help sourcing those :wink: try and avoid the situation where you have to peel them off to realign. If theres an air bubble in the middle dont worry, etchant can't get into the air pocket unless the bubble ventures near the edge of the mask.

3) Pour half a kettle of boiling water over the piece. Leave to cool. Think ive removed my fingerprints a few times through being impatient :biggrin:

4) etch away

The boiling water causes the vinyl glue to melt and really adhere to the surface, and at the same time shrinks a little in effect shrink wrapping the piece.
 

magpens

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I like this idea ! . How do you transfer the desired pattern to the vinyl ?
 
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BradG

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Hey Mal
Photo resist is a pain to apply to anything which isn't flat. I use Sign writing vinyl. see the post above for tips :)
 

BradG

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Originally I made my images in photoshop and sent them to vinyl cutter companies on Ebay, and they would cut them out for me for about £1 each. in the end I took the plunge and bought myself a vinyl plotter/cutter.
 

bobleibo

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I really like that, I think the textured part, adds character.
Just a curious question, if there's a simple answer. Knowing nothing about chemical etching, how do you control the depth of the cut? With a mechanical machine it's self-explanatory but how do you control a liquid that runs its' own course?
Cheers
Bob
 

magpens

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Good point, Bob. . You want the portions that are to be etched to be properly accessible to the etching current. . The microscopic makeup of the solution is constantly changing as the etching progresses and so the current path will also be changing. . Seems to me you need some agitation to try to keep the makeup of the solution uniform.
 

BradG

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Hey Bob
Simply by checking the piece periodically. You can keep removing the piece to take a look, and just put it back in if you would like it to go deeper.

Of course if you are using a constant current & voltage each time, you will have a pretty accurate rough idea as to how deep it will etch after 10 minutes, or an hour.

Different etchants times vary greatly. Sodium hydroxide is about 30 seconds to a depth deeper than pictured... but it does cost in resolution. great for celtic knots I found.
 

BradG

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No agitation is required for this process. just uniform cathodes.

Agitation can help with Ferric, but it adds to the mess and can cause problems with air pockets forming, which obviously blocks the etchant . Citric acid dissolved in the Ferric for an Edinburgh Etch solution works better
 

magpens

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Would it make any significant difference to have a cylindrical cathode with the piece to be etched (the anode) being on the axis of the cylinder ? ... symmetry and all that.
 

BradG

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yep that would certainly help. as you know, but for the benefit of others if the piece is closer to the cathode on one side, current will flow more on that side creating an uneven etch rate.
 

skiprat

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Brad, just for the record......
I burst into tears right at the beginning when you said......:redface:


.....I don't even want to repeat it....:eek:

......you said ......aargh....:eek: 'sacrificial stainless steel' :eek::eek::eek:

Say it isn't so.....what did the beautiful stainless ever do to you????? :mad:

:biggrin:
I'm actually very interested in this and may even have a go as I have a suitable power supply.
 
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AndyUK

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Lovely stuff Brad, clever and simple at the same time and inspiring stuff . Thanks for showing
 

Curly

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A question about the SS electrodes.

I've read on other forums that one shouldn't use SS electrodes for rust removal because it releases Chromium compounds which are bad to breathe and toxic for disposal. So does the same happen when etching or were the warnings about rust removal wrong?
 
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