Etching aluminum with Ferric Chloride

Ferric Chloride is a great substance! A lot of people have it, cause it is used to etch PCBs in DIY conditions. Aside from eating away copper, FeCl3 reacts with a lot of metals, but is harmless to most paints, even paint from a gel pen or a CD marking pen, or any alcohol based pen. And that is used for making PCBs: you clean the copper plate of the PCB, then draw the artwork using such an alcohol based paint (from a CD writing pen, or any other).

The process described here, is very similar, only it’s being applied onto aluminum. Aluminum reacts more violently with FeCl3 than copper. Hydrogen gas starts forming and the aluminum objects will get hot very quickly.

I am NOT responsible for anything that may occur to you because of following this tutorial! You will follow this tutorial at your own risk!!!

So, here it is, step by step:

0. Work with rubber gloves in a well ventilated space. Although not deadly, FeCl3 is still a chemical.

1. Prepare the surface: This is a simple one: scrub the surface with either fine smirk paper, or something like Cif Cleaning Cream. You need to clean the surface, and make it as smooth as possible. This is not a chemical requirement, but it’s an aesthetic thing. You wouldn’t want your surface to be all scratched and dented…

2. Write whatever you need there… but use negative writing. The surface that is protected by the paint will remain, the surface not covered by paint will be disolved. See this example picture:


3. Get the ferric chloride. Go buy it somewhere, or get it by other means. HANDLE IT CAREFULY! Though it is not too dangerous, it still is a potent acid, and should be handled as such!

4. Apply the FeCl3 onto the surfaces you want to etch:


To apply the acid I used a very simple wooden stick: first, I dipped the stick into a jar of the acid, then took it out. A small amount of the acid stayed on the stick. I toutched the surface with the stick, and it transfered all of the acid on it onto the aluminum.

After that, wait until the reactions comes to a halt (approx 1 minute). You can see that by observing the bubbles of gas that are created from the reaction, as seen in the next picture. At first, there’s a few, then, there’s a lot, and in the end, the rate at which the bubbles are spawned is quite slow. Be wary, that the surface will be quite hot, because the reaction is very exotermic.

Note on the bubbles rising: It’s hydrogen! DO NOT use anything around that might throw sparks! Hydrogen is extremely fun…erm…dangerous and explosive!

After the reaction has halted, take a paper napkin, or a towel, and wipe all of the acid from the surface. Then clean it with water.

NOTE: You must NOT put the whole aluminum object into any kind of FeCl3 bath! This could start a VERY bad reaction through out the whole surface, destabilize the paint and heat up very seriously!!!

Do the same for all areas on the surface, that you want to etch:


5. Clean and rub and scrub! You now should have something like this:


Note that the etched part of the surface is brown. Now you need to apply some Cif Cleaning Cream (or toothpaste should work also:-) untested) onto the surface and start scrubing it with a lot of paper napkins:


6. Enjoy the wonders of your work!


This is the result of scrubing the etched surface a few times. The brown stuff has been cleaned away and so has the CD marker paint.



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6 Responses to Etching aluminum with Ferric Chloride

  1. Larry MacCaskill says:

    Ferric Chloride is NOT an acid!
    It is a metallic salt, like the Sodium Chloride which you sprinkle on your fries
    (I would not recommend sprinkling FeCl3 on your fries, though).
    It won’t eat holes in your skin but it WILL wickedly stain your skin and your clothing brown, so be careful, keep it off you and rinse it off quickly if you get messy.

    • Kieran says:

      ferric chloride is acidic by nature though, this is due to the hydrolysis of the ferric ion.

  2. MJohnM says:

    Ferric chloride etching solution is usually a mixture of ferric chloride and an acid – usually sulfuric but can also be hydrochloric. It is a strong acid!

  3. Anders Ahlgren says:

    It is a salt, yes, but it is actually also an acid since it has low pH when solved in water (which is the definition of an acid).

    The difference compared with sodium chloride is that when hydrochloric acid is combined with sodium hydroxide (giving a sodium chloride solution) the acid and the base cancel perfectly, but if you use ferric hydroxide instead the hydroxide does not completely dissolve in water, so some of the hydrochloric is left, and the result is acidic. We are talking roughly 1% hydrochloric, for a pH of about 1.5, so it is much weaker than the really strong stuff, but also considerably stronger than, say, distilled vinegar or lemon juice.

  4. I am looking for a way to cut some intricate patterns all the way through some aluminum flashing. I have done some electro etching experiments with salt and vinegar and cotton swabs on a alligator clip and it works fairly well but is slow and I would prefer dipping in a bath. I am using the clear coating that comes on the flashing as a resist and scratching and laser engraving through that coating to expose the areas I want to cut through. I am guessing that the FeCl would probably eat through the coating (or the heat would compromise it). Do you have any suggestions for a better way to do this?

    • daqq says:

      I don’t know really, depends on the coating material. FeCl is actually pretty harmless to many kinds of coatings (lacquers, paints etc.). You will have to do some experiments I guess. Good luck!

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