Stop using Ferric Chloride etchant! (A better etching solution.)

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.

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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.)

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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)  deephidden11 hours 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.

CR9Designs4 days 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 days 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)  CR9Designs11 hours 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.

DaveSemm4 days 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 days 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)  DaveSemm11 hours 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....

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

See 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!18 days 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!!


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.
Xexos22 days 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.

TrumanF1 month 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?


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)


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.

I'm no chemist, but DO NOT MIX AMMONIA with this etching solution...

ChipBits1 month ago

UK visitors - Everbuild brick & patio cleaner (<10% Hydrochloric Acid) from hardware shops and Care+ Hydrogen Peroxide (9%) local chemist. Slow but works.

What ratio did you mix the two. I've a 6% H2O2 and a mix of 9.9% HCL (brick cleaner alright). It's turning green but it isnt etching a thing (only cleaning off the sharpie I used to fix a track on the etching).

Mine was about 3 x HCL to 1 x H2O2 by volume. I've noticed a lot of variation here and people seem to prime it with spare copper to reach optimum speed. These % mixtures are mostly water & seems a lot of people either use air bubbling, agitation or heat to either evaporate off the water or accelerate the reaction. Still experimenting here too!

Ok, to get rid of the excess copper chloride, you generate hydrogen gas and pass it over heated fine ground crystals which will reduce the copper salt to metal and give HCl gas as a byproduct which can then be bubbled into water to give more hydrochloric acid. We use to do something similar to this in the lab using zinc and hydrochloric acid and then we would pass the hydrogen through a heavy glass tube with a few Bunsen burners underneath, copper product inside. We used this to repair copper wool that had turned green and clean pennies. Most of the pennies were just oxidized with oxygen so we got out just water. Of course zinc chloride isn't very life friendly either, so maybe electrolysis of water to make the hydrogen would be better. Of course heating hydrogen gas over an open flame in a glass tube isn't to be taken lightly, so maybe you should just place the extra into plastic bottle and seal it into a bucket of concrete and take that 10 miles off shore and dump it into international waters like most industrialized countries do now. Who knows? If you survive my suggestions, later.

crazypj1 month ago

I'll try the toner transfer method to make 'real' circuit boards, this was just a thick Sharpie I picked up to test things which is why it's so rough

Cap pack 3.JPG
The Real Elliot (author)  crazypj1 month ago
Bah! That's not rough -- it looks pretty darn good. And if it gets the job done, it's more than good enough.

I do a lot of little circuits with Sharpie and etchant. It's great for quickie one-offs when it's not worth designing a whole layout, but you still need the strength and structural stability of a PCB.

It's a great trick to have in your bag, if it helps you get stuff done faster or better.
crazypj made it!1 month ago

I was astounded how well it worked. Did a very rough drawing to make a series/parallel capacitor bank using miniature 'ultra caps'.

Was real easy to solder

Cap pack 3.JPG
GeraldB31 month ago

will it work on steel painted with cellulose i.e wanting to etch on a stencil on the side of a commercial vehicle

dkoebnick1 month ago

Can you store the etchant in the container (plastic) that you are using for etching? Can you use a cover on it when storing?

The Real Elliot (author)  dkoebnick1 month ago

Yeah totally. But.

Make sure that the cover is airtight or else you'll likely get HCl fumes leaking out.

I bought a tray from Ikea that I thought had an airtight lid because it had a silicone-y gasket. Apparently it wasn't airtight. The fuming wasn't drastic, but it rusted a USB cable that I kept in the same drawer over the course of a few months.

Since then, I still use the tray for etching because it's transparent and spillproof, but I also use a funnel and pour the etchant back into a plastic drink bottle (appropriately labelled) after each use. It's not that much hassle.

Chimera Dragonfang made it!2 months ago

Had way too much fun with a bunch of the brass scrap kicking around in my workshop.

Drinks Coasters.png
zann682 months ago

I tried this method today to do a Arduino RSSI Antenna Tracker board, worked Perfectly!! Way better than Ferric Chloride method. Plus side also you can see what it's doing - Will now only use this method! Thanks!!

AKL3219 months ago

What is the best way to wash off the hydrochloric acid and hydrogen peroxide after the etching is done? Water? Would ammonia or baking soda cause a dangerous reaction?

weish AKL3213 months ago

i would just use a large water bath in a non reactive container to wash the board, then add some baking soda before dumping it out. don't add ammonia though, there's chlorine compounds in there and ammonia could liberate the chlorine gas, which is nasty in even small amounts.

raukorist773 months ago

what did you use as a resist for the etching? considering using this for some copper tubing

HassaanA3 months ago

Thanks a lot The Real Elliot. This worked amazingly well. Etched my 6x6 inches pcb in just 3 to 4 mins, Ferric Chloride used to take more than 30 mins. That is a great etchant. Much more cleaner and easier to use as compared to FeCl3. :)

jenjen.dobson4 months ago
Can this be used to etch sterling silver?
mwestern14 months ago
It doesn't surprise me that the 1:1 solution was a bit more energetic.
With the 1:2 ratio of 10M HCl and 3% H2O2, the actual molar ratio is 4:1, with the equation requiring only 2:1, so you do already have a fair bit of acid left over.

Although I'm not a chemist either ;)

Also, a minor correction (as I see it) to one of your equations:
4CuCl + 4HCl + O2 -> 4CuCl + 2H2O
Since oxygen doesn't naturally occur as a single atom :)
Mulemom34 months ago

Will the starter etchant work on brass? I'm using ferric to etch brass, but it stops working after just a few uses. If I can make the etchant cheep, I'm ok with that, but if I can make it cheep AND use it forever, well that sounds perfect! Would it work better if I dissolved some copper wire in it?

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