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Copper Etching

March 28, 2011

Copper is a really nice material: easy to work, with a pleasant appearance and with many techniques available to decorate it. One of those decoration method is the etching process: with this technique, it is possible to obtain a nice relief (like those shown in the images below). Even if, at first glance, this process does seem complicated, it is really easy.

The principle of etching is to mask out areas that should NOT be corroded, using some kind of material which is impervious to the corrosive agent. Then, the corrosive agent is used to remove copper from the unprotected parts.

Using this technique, it is possible to obtain detailed relief patterns which are especially suited for jewelry and small-objects decoration.

Small chemically-etched copper rings

Chemically-etched copper pendant

Electrically-etched copper pendant

PLEASE, BE CAREFUL… etching involves the use of toxic chemicals or the combination of electrical devices & water.

I will briefly introduce here the two main techniques for copper etching; in future posts, I’ll present actual projects done using this process. There are two ways to go: chemical etching and electrolitic etching.

Chemical Etching

Chemical etching rely on a chemical compound to corrode the copper: the most common is Ferric Chloride. The copper piece is put in a bath of this corrosive liquid and kept there until enough copper has been eroded.

The resist can be as simple as the ink from a felt pen or marker; you’ll have to experiment to find the correct brand/type of marker for your project (ink does vary a lot between brands). I used this kind of  resist on the rings and pendant shown above. Other options are a piece of tape (i used it to mask the interior of the rings and the backside of the pendant shown in the images above), nail paint or laser-printer toner (I’ll post a tutorial on this).

The etching agent can be found as a liquid or as powder/pellets to be dissolved in water. The liquid version is stronger, but the solid one is much much cheaper. Instruction on how to use the liquid or how to prepare the solution are generally on the product box.

Both version. I got mine from an online electronic supply shop, but most electronics supply store (like Radio Shack) should have this kind of products available. I used Iron(III)-Chloride (FeCl3) in pellets 56% concentration: to obtain a suitable etching liquid, i mixed 500g of pellets in 0.6 liters of water.

The time required for etching does vary a lot: it depends on many factors such as copper hardness, the extent of the surface to etch, the “freshness” of the liquid and other factors. I recommend to wait some minutes (at least 5-8) and then check the progress regularly (every 3-5 minutes).  On the objects above (rings and pendant) it took between 10 and 20 minutes to obtain such level of etching (around 0.5 mm).

The container for the bath may be anything made of plastic or glass (avoid metals, they can react to the corrosive agent). I have a plastic container for flat pieces and a glass jar where I can suspend small jewelry and have the liquid work on all sides.

Bath for chemical etching

  • The etching liquid can be re-used, but every time it will lose a bit of its effectiveness (making the process slower), until it will no longer work. New liquid is light-brown, spent liquid is dark yellow/green with lots of dense residues on bottom of the tank.
  • Agitating a little the tank (to have fresh liquid in contact with the copper at all times) can help in speeding up the etching and in obtaining a sharper result.
  • Etching liquid works faster if it’s hot; not lava-scorching hot, just around 40° – 50° Celsius. I normally prefer to go slowly with the room-temperature liquid, since too much heat can damage the resist and make your design less defined.
  • The amount of etching liquid you used is not really much, it may be disposed in your toilet. It is recommended, before disposing it, to neutralize it by adding to it a  spoon of baking soda.

Be careful! Etching liquid is toxic (do not use containers you use for food), not really good for inhaling (do not put your head above the etching bath) and it is able to stain almost any surface. Wear gloves and, possibly, some kind of protective eyewear.

Electrolytic Etching

Electrolytic etching works by using direct current and a solution containing copper ions, exploiting the process of electrolysis. The piece to be etched is connected to the positive terminal of a power source, while the negative terminal is connected to a scrap copper piece. When current is flowing, copper ions are removed from the positive terminal where they are in contact witht he solution and go towards the negative terminal. Similarly to the chemical etching, by masking the areas we do not want to be corroded, we may control the etching pattern.

In order to electrically etch, you will need a device able to produce current: there are, available on the web, some electrolitic etching kits, like this one. However, in the end, those devices are basically just power transformers (plus current/voltage regulators) which is the same thing as a power adapter. I then selected one of such (a leftover for a set of PC speakers) which had a suitable power output (5 Volts and 1000 milliAmps), and from the outlet jack I extended two cables to use as terminals. I chose on purpose an adapter with very low output, to be sure of avoid any possible danger. Another (safer) option is to use a small battery: “transistor”-type 9V batteries are fine, consider using rechargeable batteries to avoid spending an insane amount of money on batteries.

I fixed the POSITIVE cable to the object to be corroded using some insulation tape, obtaining the ANODE, and the NEGATIVE cable to a scrap piece of copper to be used as CATHODE . When doing this, be careful to completely seal the contact between the positive cable and the copper piece to be etched, otherwise the corrosion will eat away the cable (at an amazing speed), instead of the copper piece 🙂 (i discovered it the hard way).

Etching should happen in a liquid where there is already some free copper, in order to start up and help the flow of ions. This is done by dissolving in water some copper sulfide.  Where to find copper sulfide? This is easier… any shop selling plant and gardening will sell copper sulfide, and it is really cheap. To prepare the etching liquid, dissolve in water copper sulfide until the solution is saturated (add and stir a spoon at a time, until it is impossible to dissolve any more of it). After the etching, the liquid for the bath can be disposed without problems in your toilet (again, the amount of chemicals you are throwing away is not that much).

Electrolitycal Etching bath

When the two cables are connected put everything inside the copper sulfide solution and connect the power source. You should see bubbles forming around the terminals, this   . After a while, you should see the cathode terminal getting darker and larger, as copper flakes are deposited on it; shake it a bit to remove the accumulation. DO NOT let the two terminals (the copper piece to be etched and the cathode) to touch !!! this will close the circuit and overheat/damage the power adapter, this may lead to skin burn, failure of your house power line, fire and/or explosion of the power adapter.

In this case it was harder to find a good resist, ink from felt pens and markers just dissolved in the solution thanks to the bubbling reaction. I resolved in cutting masks out of tape… this gave me less fine control over the design, but resulted in more defined lines and more geometrically-looking patterns, which were not bad at all. On the other and, Laser-printer toner does work fine.

As in the chemical process, wait some minutes (5-10) then check regularly the etching process, until the desired amount of copper is removed. The electrically-etched pendant shown in the image above has been done in two separate etchings (one for each half) and each one took 20-30 minutes (the play-it-safe power adapter is safer to work with but it is sooo slow).

Again, electrolytic etching can be dangerous, since it involves electricity and water. If you are unsure on what to do, try using one of the kits available on the web (instead of building some dangerous contraption).

What to Etch ?

There are many options…

PCB boards, the copper-plated resin surfaces used for building electronic circuits are an excellent choice:  They come in different size and the thickness of the copper layer is so small that very few etching liquid is required. They are really good for printing a photo in copper (I’ll post a project about this).

A copper-etched photo

Copper is nowadays harder to find, given the raise of its price on the market due to increased demands for electronics products. It is possible to find copper plates in art shops (with various thickness and sizes). In DIY and home improvement shops it is possible to find copper tubes (good for rings or, cut and flattened, for anything else)  and small things like copper washers that, with some effort, can be turned in jewelry trinkets (again, I’ll post something about this in the near future).

Etching will also work on brass (quite well) and, changing the chemical, on silver (but i never tried it).

Etched Brass bracer

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