Picture of Stop using Ferric Chloride etchant!  (A better etching solution.)
Ferric chloride is a traditional home-use circuit board etchant. It's easy enough to come by, and the Ferric by itself is no big environmental problem. However, once you've etched a board with it, you're left with a solution with a bunch of copper chloride in it. This dissolved copper is an environmental problem, and you can't just pour it down the drain (legally) -- you're supposed to take it to a hazardous waste facility. (For instance: How to Dispose of Ferric Chloride in this FAQ. )

Wouldn't it be nice if there were an etchant that you could re-use indefinitely so that you don't have to worry about disposing of the copper, and that could be made in lifetime supply for like $10.00 with ingredients bought at hardware and drugstores? (And it's prettier too.)

I got seven words for you: Copper Chloride in Aqueous Hydrochloric Acid Solution! (Exclamation point!)

But how're you going to get CCiAHAS? Conveniently enough, by starting out with a simple two-ingredient starter etchant, and doing a bunch of etching.

Step 1: Ingredients: The Starter Etchant

Picture of Ingredients: The Starter Etchant
For the starter etchant itself, you only need two ingredients: hydrochloric acid and hydrogen peroxide.

(OK, actually three. But the third one's copper. See the chemistry section for an explanation.)

Hydrochloric (muriatic acid, "pool acid", etc.) is available at a hardware store. The acid I got is 31.45% (or 10M) and should run around $5 per gallon. Which is more than you'll ever, ever need.

The peroxide is normal 3% for mouthwash or cleaning cuts, and can be bought at a drug store for $2-3 for a big bottle.

You'll also need a non-metallic container that fits your PCB and two standardized measuring cups.

As long as you're in the hardware store, pick up some acetone if you don't already have some. It's useful for removing the etch resist. (That's for another instructable.)

Step 2: Put the Lime in the Coconut...

Picture of Put the Lime in the Coconut...
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Measure out two quantities of hydrogen peroxide and pour it into your non-metalic container.

Measure out one quantity of hydrochloric acid and pour it in. ("Do like you oughta, add acid to water" to minimize the chance of an out-of-control exothermic reaction.)

Be careful with the acid. This stuff (at 10 molar) is strong. Mine fumed a bit when I took the cap off. Don't breathe it directly, and be sure you've opened the kitchen window.

The starter etchant you've just made, on the other hand, is not so bad -- around 3M HCl with a medium-strong oxidizer. I find it doesn't fume much at room temperature when I'm re-using a batch.

That said, you've got to be very careful to keep it away from metal -- especially your stainless-steel kitchen sink. It'll eat the stainless coating right off. Keep plenty of water flowing at all times when you've got any of this (even a drop) near the sink.

Step 3: Add PCB and you're Etching.

Picture of Add PCB and you're Etching.
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Toss the PCB into the solution and it'll take off.

If this is the first time you're using this batch of solution (and I presume it is), it'll etch super-fast. This small board took only 2 minutes. Yikes!

Since I use a deep container, I tend to swirl it around as it etches. This stuff is so active, though, that I'm not sure it's necessary.

Keep the window open for ventilation because the starter solution gives off a little chlorine gas. (The end-etchant gives off much, much less.)

Also, note how the etchant gets greener over time as it eats away the copper. This is good news.

What's happening is that you're dissolving the copper from the board and turning it into cupric chloride. In the long-run, the cupric chloride will be doing most of the etching (instead of requiring disposal). For now, just watch your solution turn light green. Next time you use it, the color will deepen.

Step 4: Chemistry Break

Picture of Chemistry Break

(Note: I'm an economist, not a chemist. Please leave a comment if you've got any corrections and/or additions to this stuff!)

I stumbled on this idea when I saw this website: Etching with Air Regenerated Acid Cupric Chloride by Adam Sechelle. Cupric chloride can be re-used indefinately by topping up the acid levels and adding oxygen (bubbled in from the atmosphere). Sounds cheap and environmentally friendly to boot.

The website's got a lot of good chemistry info on cupric chloride etching. His data on etching speeds is great, and his simple titration procedure for maintaining the acidity of the solution is pretty nice.

To make the cupric chloride solution, he dissolves a bunch of copper wire in hydrochloric acid, and mentions maybe using hydrogen peroxide to speed up the oxidation, but doesn't go into detail.

Which got me thinking. You didn't have any cupric chloride yet, but you can make it by dissolving copper. Dissolving copper is the name of the etching game. So we can make one etchant that makes another etchant that's infinitely re-chargeable. Elegant.

Turns out that hydrochloric/peroxide is a common home-brew etchant (and I've re-re-invented the wheel, again) but I guess that people got so used to throwing away their "spent" etchant that they don't think about re-using it. The whole point of this instructable is that you don't throw it away, but use the dissolved copper forevermore as your long-run etchant.

Here's what's going on chemically:

Before there's much copper dissolved in the solution, Cu + 2 HCl + H2O2 -> CuCl2+ 2H2O is the dominant net reaction. That is, the extra oxygen in solution from the peroxide is oxidizing the copper metal, in presence of the acid, to make copper (II) chloride. That's our starter etchant. The resulting CuCl2 shoud be a nice emerald green color.

After you've dissolved a lot of copper into the solution, and used up all the peroxide, the copper chloride does most of the etching for you: CuCl2 + Cu -> 2 CuCl. That's the end etchant.

Eventually you etch so much that you convert all the CuCl2 into CuCl, which doesn't dissolve copper (and is a yucky brown color). As long as you've got enough acid in the solution, you can simply add more oxygen to re-oxidize the copper(I), making more copper(II) chloride and water: 2 CuCl + 2 HCl + O -> 2 CuCl2 + H2O. And then you can etch again.

Bottom Line:

Two things to maintain: CuCl2 levels and acid levels.

CuCl2: After all the peroxide is used up, and the solution starts turning brownish, you'll have to add oxygen to regenerate the solution again: toss in a few more capfuls of peroxide or bubble air through the solution or swirl it around vigorously, or just pour it into an open container and wait. It's easy to tell when you're ready to etch again, because the solution turns green.

It's also impossible to add too much oxygen by adding air, so bubble/swirl to your heart's content. If you're using peroxide to add oxygen, be sparing -- a little goes a long way, and it's mostly water so you're diluting your etchant by adding it.

Acid: Note that HCl is being consumed in the starter etchant and the regeneration reactions. So we're going to have to add a bit more acid as time goes by. If you notice that it's harder to re-green your brown etchant, it's probably time to start thinking acid.

I've tried the titration described on Adam's site a couple times, and it's pretty easy but requires an accurate scale and pure lye (back to the hardware store...). It's easier to just toss in a capful of acid every few batches of boards, which seems to do the trick for me.

Step 5: Save the etchant for next round. You're done.

Picture of Save the etchant for next round.  You're done.
Once you're done etching, pour the etchant back into your storage bottle, rinse off the board, flux, drill, populate, and solder.

Some final notes here:

1) You can make quite a bit of this stuff very easily, and since you're re-using it, there's no real reason to skimp; put plenty of etchant in your "tank." When you use too little FeCl etchant, for instance, it can get saturated with copper and slow down which can result in long etching times and pitting or undercutting or worse. When I'm etching a board with copper chloride, I'll pour a couple extra inches of solution into the container. It's reusable anyway, and the extra exposure to oxygen just regenerates it. Live large.

2) Don't make too much. As you keep re-using the solution, you're going to need to add a little more acid and a little more peroxide every once in a while. If you've got a 750 milliliter container, start out with less than 500 milliliters of solution. Give yourself some room to grow over time. After all, the main point is to avoid having to dispose the copper in spent etchant.

3) If you've got too much volume of etchant (it will happen eventually) you can evaporate out the extra water by putting it in a shallow (non-metallic) pan or beaker or whatever and letting it sit for a while. This concentrates the copper in solution, giving you a stronger etchant. It'll also re-oxidize some of the copper for you, a bonus. Remember when you're adding the peroxide that you're actually adding 97% water.

4) The linked website suggests that the acid levels in the etchant are not critical as long as there's some acid in solution to do the CuCl2 regeneration. The amount of CuCl2 (vs CuCl) present is easy to diagnose by the color of the solution. Add oxygen to re-green, and add a bit of acid if that's not working. Worst case is that you may have to wait a few more minutes per etch with a sub-optimal bath. This isn't rocket surgery.

5) I do have an aquarium pump ($6 at fish store) that I've used to re-activate my solution. Sometimes I'd leave it on for a few hours while I'm at work if I've been etching a lot. But lately I've been lazy/impatient and tossed in a couple capfuls of peroxide. Both seem to work just fine.

6) The environmental benefit of etching with copper over ferric lies mostly in not having to dispose of the copper that comes off your boards every few times you etch. When and if you do end up with too much copper etchant, please treat it like the hazardous waste that it is -- look into your local hazardous chemical disposal options. There's no getting around the fact that copper salts are (for instance) poisonous to fish even in very dilute concentrations.

Step 6: Alternative (overly-complex) Method: Make Cupric Chloride Faster.

When I originally started trying to make Cupric Chloride etchant, I hadn't thought of just using the regular procedure of etching to get there. So I deliberately dissolved a bunch of copper from a wire.

I don't think it's a particularly good idea, but here's how I got to the end-stage etchant faster.

I mixed the acid/peroxide 1:1 instead of 1:2. The idea was to have a bunch of acid leftover for later regeneration. I don't think it's a good idea, and I wouldn't do it again. 1:2 is probably better, and results in more copper in solution faster with less fuming.

To control the fumes, I used the patent-pending (just kidding) Two-Pint-Glass Fume-Containment-Apparatus. Pour in the peroxide, add the copper, then put one glass on top of the other. Pour the acid down through a small gap between the two glasses and re-seal. Voila. No fumes. (See video. I think I did it with water as an example.)

I also kick-started the formation of cupric chloride by first making copper oxide, which turns to cupric chloride just in the presence of acid alone. This isn't necessary at all, but it was fun. Heat up a coil of copper wire on the stove to red-hot and you get a flakey coating of copper oxide.

Otherwise, it's basically the previous procedure, so just see the pics for notes. I wouldn't recommend it anyway. The less copper you dissolve, the less copper needs to be (eventually?) disposed of, and the acid/peroxide etchant is plenty easy to use.

The two-cup technique is cute. I still recommend it.

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Rouverius11 days ago

Thanks for this. Off topic but your storage bottle reminded me of this... http://drunkard.com/images/scottie-hooched.jpg

Liamthe1st17 days ago
I am now confused. after reading so many comments I just want to do a PCB for a small electronic circuit.
what my board is two inches by one inch . seven components four wires it is a light activated
this phone is stopping me from asking the question what is the amounts in Mililtres cups are not standard in UK
hhissi1 month ago

I live in a place where it's impossible to get acids from a drug store. I can only find acids used in detergents or other cleansing material and so forth. So im wondering if there is any product at a normal market that could be used instead of hydrogen peroxide and hydrochloric acid?

Search for vinegar/peroxide/table salt mix. It's about 100ml/100ml/10ml
The Real Elliot (author)  hhissi1 month ago
Chemistry supply house? Hardware store? Or beauty supply store for the peroxide?

Hydrochloric acid is pretty common. It's used to balance the acidity of pools and to clean concrete. I don't know where you live, but I bet you'll find some.

The peroxide I used was really weak -- the kind that people often use as a mouthwash. But stronger peroxide mixtures are commonly used to bleach hair, for instance.

I'd avoid anything with additional additives. You just don't know what will happen.

(For instance: some people have substituted mostly-NaOH drain cleaners for NaOH, but then it's also got some aluminum flakes in it which make the reaction exothermic, and turn something potentially simple into a safety hazard.)

Look around more and get the pure stuff.
MichaelJ311 month ago

So I made a batch but am curious about my storage container. Its a glass jar with a glass lid an rubber seal that is closed with the clamp. Hopefully you know what I'm talking about. Will this be okay? I just don't want gasses to expand an compromise anything/break the jar.

PerchE1 month ago

So .. pool acid and mouthwash.
I read in the Ferric Chloride FAQ, that I need Washing soda >> is it enough of the materials you mentioned ?
And, how to test it with a paper ? normal paper and what's the sign that the mix is safe to pour?
Thank you,

The Real Elliot (author)  PerchE1 month ago

Don't go substituting stuff! (Unless you really know what you're doing.) Hydrogen peroxide _is_ used by some folks as mouthwash, but that doesn't mean any other mouthwash will work.

Hmmm... washing soda. I'm guessing that's to neutralize the acid for disposal? If so, part of the point of this etchant is that you will not need to get rid of any of it for a reasonably long period of time (years? a decade?) because it's renewable. So you shouldn't need that.

And anyway, I'm not sure that knocking down the acid makes it safe to "pour". You'll end up with a different copper compound, but it's the copper that's bad for water sources.

I think when people dispose of stuff this way, they neutralize it first and then let it dry out, and then take it somewhere where you can dispose of hazardous chemicals. But again, we're trying to avoid doing that in the first place.

SaraS151 month ago
Is this method just for making PCB or could one use this mixture for etching copper jewelry?
geo bruce made it!2 months ago

Thanks works great!!

I've made a mixture of: 1 cup H2O2 36%, 1 cup HCl 23%
and made a simple test pcb. I did nothing to start the process first try was slow but second try was much faster. Because there was already some copper in the mixture.
I was able to make a trace of 12mill => 0.3mm, my printer was the bottle neck.

20150619_223757.jpgtest pcb.png
Richard 112 months ago

made this etchant, it worked very quickly clean, no fumes excellent.

Thank you for your project, looks like a good system to me. Do you have a recommendation of what types of plastic I could use as containers for this project? I intend to use it to electroplate graphite painted 3d printed plastics such as PLA/ABS/HIPS/Nylon/TPE, can you think of any issues i might face with any those plastics?

compwolf3 months ago

Just one quick question, does the container need to be actively open when using the solution? The reason why I ask is I try to minimize any fumes I can (even when soldering). Like using a small glass pan with modified lid that locks everything air tight as it etches. I don't know if its like a fume pressure build up like smoke would cause, or more extreme like a 6th grade volcano kind of pressure. Thank you.

The Real Elliot (author)  compwolf2 months ago

No problem closing it up as it etches. I always do that so that it doesn't spill while I'm agitating. (I etch in tupperware and slosh it around vigorously.)

Ziplock bags also make a nice etching tank. Board in, fill with etchant, close, and then lay it all flat in some kind of dish or tupperware in case you accidently break or open the bag. You can agitate the board by smooshing the bag (carefully) like a waterbed, and it's really easy to tell when it's done because you can press the bag up against the board like a window.

The other advantage of the tupperware + ziplock bag is that you can easily fill the tupper with warm water which will keep the etchant warm and speed up the reaction.

When you're done, snip off a corner from the bag and you've got a funnel to pour it back into your container.

Man, I should make an Instructable on that...

AlexeyM12 months ago
For etching Cu try H3Cit + H2O2 with NaCl.
deephidden3 months ago
I think I used too much. All I did was create fumes are irriate my breathing. I'm going to toss the batch, air out my house and try again actually using you measurements. I've gotten too used to just winging it on the amounts of things I use.
The Real Elliot (author)  deephidden3 months ago

Too much what?

Just aim to get the acid down around 3M or 10%. So if you start with 10M / 34% acid, you need to add two parts water (or weak peroxide in our case).

Mixing a strong acid and water like this makes heat. If you toss water into the acid, you'll get hot acid and that might fume. Don't do that.

Measure out two cups of peroxide, pour into that one cup acid. Easy enough, but you need to measure and get the order right.

Open a window anyway, and if you're getting excessive / noticeable fumes rethink what you're doing.

And if you want to ditch a batch of the etchant before use (no copper dissolved in it yet), you can toss some baking soda into it to neutralize the acid and pour it down the drain with a lot of running water.

can i use sulfuric acid 30% instead of muriatic acid?
The Real Elliot (author)  Testas.T3 months ago

Not 100% sure, but I'd say no.

TrumanF5 months ago

Elliot the first time I tried this is worked flawlessly. Now I used a small tupperware leftover tub and the boards etched in just a few minutes. I tried it again two nights ago, which was a few weeks later and tried using the still very green solution but I played heck trying to get it to etch. I added a bit more acid but it only seemed to work once I added a little more H2O2. The color didn't change much but the board started losing copper at a more normal rate. Since I bought a laminator and couldn't wait to try it out again last night I threw a couple of small boards in the day old solution and the same result. Just wouldn't etch. Left it in for an hour just to see what would happen and nothing. Added more acid and unfortunately I was out of H2O2. The solution was still nice Kool Aid green too. My wife is picking up some HP today at the store and hopefully when I add that the magic will happen once again. The container is only 4 inches square and maybe 1.5 " deep. You think I should use a larger tub?

DaveJ1 TrumanF3 months ago

Same boat, friend! First batch etches like a dream, but subsequent etches, even if same day, don't complete. Seems a bit of a waste if we have to top off with acid AND H2O2 each time (might as well start from scratch, negating the potential environmental benefits)...

fkahhaleh TrumanF3 months ago


I am having the same issue as you are, my initial solution was PERFECT.

I leave it for a few months, not needing to do any PCBs, come back to it and it is barely etching. I used the "bubble in air" method with no luck, out of HP and will grab some but it seems it is only a temp. workaround and not a solution to the problem.

Were you able to figure out what was wrong? (solution color is LIGHT GREEN)


DaveJ13 months ago

Help! My attempts only work when I start fresh with HCl and H2O2- when I try to reuse the beautiful emerald green solution, it stalls, and gives me a very bad etch! My solution isn't turning brown, so it has enough oxygen, and it still takes to copper to the rosey stage, so i think it has enough acid. I will try adding more acid, but...

CR9Designs3 months ago
I mixed the acid and peroxide in the correct ratios. I used my vinyl resist and let a piece etch. It wasn't very deep after an hour so I removed the piece. I placed a couple of scrap pieces in the solution for a few hours and they reduced in thickness quite a bit. I then tried etching another piece and it seemed to be slower than the original etch attempt.
The solution is still a very light bluish green. Do I need to dissolve more copper in it first?
The Real Elliot (author)  CR9Designs3 months ago

Blue usually means copper hydroxide, which means that you've not got enough acid in the solution. I'd pitch in a little bit of acid and see.

How much copper were you initially etching? Was this a PCB or something else? ("Scrap pieces" of what?) It may just be that you've run out of acid.

Indeed it was not a pcb. 16g copper sheeting is what I use in my jewelry making. A piece approximately 1" by 2" with a vinyl resist. It made a decent visible etch initially. I added a I" piece of 1/4" tubIng and about a 1" square piece of scrap to see if that would green it up. Those were quite dissolved after a few hours but after that nothing else would really etch.
Thanks. I'll try more acid. Would a 1/1 ratio be better for my needs?

Added a sample of the pieces I'm making. Some of those were done with ferric.
The Real Elliot (author)  CR9Designs3 months ago

Yeah, you might try a 1/1 ratio for a new starting batch, but at this point you can just top up with a little more acid and see how it goes. The whole point is to avoid re-starting and having to dispose of the copper solution.

Maintaining the chemistry (read: enough free acid & oxygen) is part of the trick with this stuff. When brown, add peroxide. When slow / blue, add acid. Easy enough once you get a feel for it.

DaveSemm3 months ago

My first attempt failed. I used 200ml pool acid (30% HCl) and hydrogen peroxide (400ml 3% H2O2), and after 20 minutes it turned slightly green, and that was it. After 2 hours there is no sign that the copper is coming off of the PCB. I kept it warm and swished it around for the 1st hour, but it looks like nothing is happening to the board; I just left it outside for now - I'll check it in the morning. I need to get more H2O2 to try to tune the batch, but if that doesn't work, I'll have to go back to ferric chloride.

The Real Elliot (author)  DaveSemm3 months ago

An hour with agitation is waay too long. Especially with fresh chemicals, it should go relatively fast, like ten minutes or so. You can tell it's etching when the shiny and coppery-colored metal goes in -- in a minute or so, it'll turn a matte pink color.

Could anything be coating the copper? Try scrubbing the surface with a bit of sandpaper (finer grit is better for not leaving scratches, but if this is just a test...) beforehand?

I've just finished successfully etching my first board! Someone suggested that the peroxide I bought might be dud: even though I bought it new, if the bottle wasn't properly sealed and it had been on the shelf long enough, he said it could be useless - it had happened to him more than once. So I bought another bottle from a different shop, and hey presto! the board etched in a few minutes. I over did it a little bit, probably because I didn't agitate it evenly: I had to wait for a patch in the middle to dissolve. (Don't swirl: rock!) But it works, so from here it can only get better. I think my main lesson is to keep a few bottles of peroxide handy.

BTW, before my 2nd attempt, I was also wondering if the "gloss" from the glossy paper might have coated the board with an invisible layer of plastic - it seemed possible - but I've now established that that is not the case. The paper works perfectly.
The Real Elliot (author)  DaveSemm3 months ago

Hey fantastic! I'm glad to hear you got it working, and even more stoked that you found a way that things can go wrong. :)

Peroxide has a shelf life, for sure. And as you note, a trip to the pharmacy and a couple of bucks can test that hypothesis.

Re: agitation is key. The center pretty much always dissolves more slowly than the edges, no matter how you agitate (unless you're spraying, but that's another level of complexity altogether). If you let it sit for a second or two, then swirl, you can see brown/black dust coming off the board -- gives you a good idea of whether you're agitating well enough.

Glad you got it working, and thanks for coming back with the report. Watch out for bad/expired peroxide, y'all!

i use ammonium persulfate. It is in powder form and you mix it with water. It is tranparent so you can see the etch working, it turns slightly blue as etch is working - I use it for etching copper bullet casings, holding the casing with a 'third hand' and putting it into a plastic up with the etching mix. you can see how deeply the etch is going and then pull it out - no fumes, no fuss. I have tried many resists, staz on ink pads with art stamps, black and white prints on photo paper which i then iron onto the casing, hand drawn sharpie pen shapes.... https://www.youtube.com/watch?v=TLf4w1zTpkw

Ammonium persulfate is great, but how you dispose of the resulting copper-containing mess is the problem.

See http://pcbhowto.com/articles/copper-etchants for what I mean.

With the cuprous chloride solution, you only have to dispose of the etchant/copper mix once: when you're never going to make any PCBs anymore. Otherwise, you can keep re-using the solution indefinitely. It's just a lot less hassle.

melissalyndell made it!3 months ago

Wow, super quick and easy!

I made this ring out of 18G copper sheet and used heavy body acrylic paint for the resist. I'm not entirely happy with the resist though as I would like a deeper etch but the paint began lifting.

Any suggestions on what to use as a resist for artistic purposes?

Thanks for the tutorial!!

The Real Elliot (author)  melissalyndell3 months ago

Wow, that's a fantastic result! (And so far away from the boring PCBs I run.)

A resist for longer-term / deeper cutting? Not sure. I've used nail polish sometimes when I need it to hold. Just have to make sure it's fully dry before etching -- a hairdryer can help. But I don't know if you'll get fine enough lines for what you want.

You might look into what engravers use? Sometimes they use some pretty nasty acids, and have a long history of high-resolution resists.

I use vinyl cut on a silhouette cameo machine as a resist. It has worked with electro and chemical etching.
Xexos4 months ago
Can this be used for damascus steel? Ferric chloride works, but it is rather expensive to buy enough to dip a whole blade in.

you dont need to dip the whole blade in a pool. Think of a sock and foot/leg. Get a plastic tube container just big enough for it (PVC tube?). you can fill the empty space with a long dowel cut in half. that way its just the blade that is covered in a few MM of liquid.

hope this was not too confusing and inspires you.

mchagerman2 years ago
When you get to the point of too much solution, you could electroplate the dissolved copper onto a piece of copper wire.

Raise the pH of the solution with lye or ammonia (to at least pH 7), stick in a copper cathode and a sacrificial anode, and apply a few volts. You'll want a corrosion-resistant anode, and platinum is rather pricey; perhaps a carbon anode would work?

It'll work better if you agitate the solution while plating.
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