Etching with caustic soda - advice

lmorse · January 17, 2015, 01:06:11 AM

I have just tried my first enclosure etching with caustic soda. I followed this advice:

http://diy-guitar-effects.tumblr.com/etching

40g to 100ml cold water. I found that within 30 seconds the enclosure was too hot to hold with thick rubber gloves on. I took it out to let it cool a little, lots of fizzing etc. So I dunked for another 30 seconds. This time when I took it out of the solution it was so hot that the toner had started to melt. So I have decided to abandon, sand down and start again.

Anyone with a similar experience? Should I dilute the solute a little more?

italianguy63 · January 17, 2015, 02:29:53 AM

Probably. I haven't gone the caustic soda route yet. Bought some, but haven't done it.

I am still doing the pool acid and peroxide mix. But, when I started with the pool acid, I had the same thing... too hot. I have diluted it down 2/3rds. Now, I do about 15 seconds at a time-- it still fizzes and gets warm, but not violent like before. My total etch time is 2 to 3 minutes in 15 second intervals. Dunking and brushing with at toothbrush in between etch dunks.

MC

psychedelicfish · January 17, 2015, 02:49:58 AM

Quote from: lmorse on January 17, 2015, 01:06:11 AM
Should I dilute the solute a little more?

You should dilute it a lot more. 40g in 100ml makes 10 mol/L, which is an extremely strong solution. I would try something more like 5g for 100mL of water, which will etch slower (giving you a better result) and be safer.

lmorse · January 17, 2015, 03:05:42 AM

Cool, thank you. I'll dilute.

Brisance · January 17, 2015, 10:38:56 AM

Am I the only one strongly bothered by the linked article calling it an acid etch and then using a strong base?

lmorse · January 17, 2015, 04:29:22 PM

Well noticed!

Pettol · January 20, 2015, 12:59:00 AM

I use NaOH all the time (30-50%) and in my experience it doesn't give more an exothermic reaction than with acid.

But when dissolving the caustic soda in water it gets very hot. Could that be it, that you didn't wait long enough between dissolving the NaOH and etching?

lars-musik · January 20, 2015, 03:21:01 AM

Hi Pettol,
is it right that you sink about 400g (for 30%) to 750g (for 50%) of NaOH in one liter of water for your etchant? That seems to be a quite a lot! But your etches look so brilliant that I'd like to go with your recipe.

newperson · January 20, 2015, 03:37:20 AM

nice write up.

Pettol · January 20, 2015, 09:29:34 AM

Well, first you must define %, v/v (not applicable here), w/v or w/w. I prefer w/w, so a 40% solution would be 40 g NaOH and 60 g water.
But in the end it really doesn't matter. You can probably etch with 10% too.

BTW, this is my recipe:

Brisance · January 20, 2015, 10:43:09 AM

with water, w/w and w/v are exactly the same.

Pettol · January 20, 2015, 11:18:12 AM

Quote from: Brisance on January 20, 2015, 10:43:09 AM
with water, w/w and w/v are exactly the same.

You're assuming a constant density of 1 kg/l. At 50% NaOH it's 1.5 kg/l.
But like I said, it doesn't matter in the end.

PRR · January 20, 2015, 02:00:24 PM

> I followed this advice:

I *believe* the (now dead) link is to a prepared "Caustic Soda Cleaner Degreaser Sanitizer", which may be much less than 100% NaOH. Drain openers are commonly mixes of several chemicals and fillers.

Replacing 50% NaOH-mix with pure NaOH will give a solution twice as strong (and dangerous!) as he used.

Add water until aluminum foil does not violently disappear.

Brisance · January 20, 2015, 04:15:46 PM

Quote from: Pettol on January 20, 2015, 11:18:12 AM
Quote from: Brisance on January 20, 2015, 10:43:09 AM
with water, w/w and w/v are exactly the same.

You're assuming a constant density of 1 kg/l. At 50% NaOH it's 1.5 kg/l.
But like I said, it doesn't matter in the end.

Aint w/v considered before mixing them together? Might be my brain telling me, that averaging 6h sleep per night is not enough though.

And also, drain cleaners AFAIK also contain some inhibitors to slow the reaction.

Pettol · January 20, 2015, 04:39:09 PM

Quote
Aint w/v considered before mixing them together? Might be my brain telling me, that averaging 6h sleep per night is not enough though.

That wouldn't say much once you have the solution and the volume has changed, would it?

Quote from: PRR on January 20, 2015, 02:00:24 PM
> I followed this advice:

I *believe* the (now dead) link is to a prepared "Caustic Soda Cleaner Degreaser Sanitizer", which may be much less than 100% NaOH. Drain openers are commonly mixes of several chemicals and fillers.

Replacing 50% NaOH-mix with pure NaOH will give a solution twice as strong (and dangerous!) as he used.

Add water until aluminum foil does not violently disappear.

I'm not sure what you mean with 100%. NaOH is a solid. 50% is (close to) a saturated solution.

I'm sorry I got into this discussion.
My main point is actually that you don't need a magic recipe to work with NaOH. It's forgiving an gives very clean etches.

lmorse · January 21, 2015, 12:57:26 AM

Paul:

Quotea prepared "Caustic Soda Cleaner Degreaser Sanitizer",

It is a prepared cleaner, it states 94% NaOH on the pot. It is the 'purest' that I could find locally. I also found that once it heated up, the nail varnish started to melt. I assume that this might be the other 6%?

Pettol:

Quotewhen dissolving the caustic soda in water it gets very hot.

The solution was not hot until I dunked the enclosure.

I diluted with an additional 3X water to give approx. 10%, and the reaction became quite slow, so I upped the strength to around 20% and it worked OK-ish, I got an etch only just deep enough in about 10-12 minutes. Like I say, the nail varnish started to melt, so I chickened out and ended the etch there. Reasonably happy with the results, the worst pock-marked areas are where the nail varnish was (I assume the solution pooled under the damaged nail varnish).

I will definitely use NaOH again, and maybe not use nail varnish.

Pettol · January 21, 2015, 02:58:59 AM

Just some comments/advice.
For a normal etch I pipette the NaOH-solution only onto the areas to be etched. That reduces the heat problem I suppose (though I haven't experienced it work reversed etches either

)
Nail polish won't work as a mask. I have had troubles finding a paint that does, but just recently tried Humbrol Enamel and it seems very promising.
I just etch for a couple of minutes at the time. Then I wash with water, examine the results and continue if necessary.

Good luck!

Brisance · January 21, 2015, 03:44:02 AM

At least for FeCl₃ and HCl/H₂O₂/CuCl₂, regular CD marker works very well!

Pettol · January 21, 2015, 07:09:26 AM

Yes. But very few paints and markers are base resistant. Bases are the main components in many paint removers...

joeowens994 · February 04, 2015, 01:53:51 AM

An idea on the paint for use as masking: etch primer.

I have been trying various different ideas for masking off the sides of my enclosure as I invariably get some of the caustic getting under the tape I use and etching the sides slightly. Today I tried this: http://www.supercheapauto.com.au/online-store/products/SCA-Etch-Primer-400g.aspx?pid=288525#Recommendations and it seemed to work. I plan on testing it a little more in my next build so I'll confirm then whether or not this works 100% but for now this looks the most promising for me. I let it set overnight before I etched, so that might've helped as well.

It also comes off easily with acetone, so clean up is pretty simple.

News:

Etching with caustic soda - advice