Dissolving salt and copper sulfate in hot water. Agitation with squeegees or brushes helps to fully dissolve the solid salt particles. Only dissolved salts provide metal ions and an electric charge crucial for etching. Best wear goggles and a dust mask when handling copper sulfate.
TIP: Using and Purchasing Copper Sulfate
Safe to Use: Use it Safely!
Remember, Copper Sulfate is still a chemical and toxic to humans if ingested, so make sure you follow safety instructions and read MSDS sheets prior to use. Always wear gloves, goggles and a mask when handling any etching chemicals. Do not touch, inhale or ingest.
Safe to Ship
For the printmaker who wants to use the Saline Sulfate Etch, getting hold of small (rather than industrial) quantities of Copper Sulfate is easy. I recently ordered a 5lb bag of Copper Sulfate Crystals over the internet. Because it is a low hazard material, the delivery came by ordinary mail services - simple, safe and economical too. No need for the specialist carriers required when shipping traditional printmaking mordants.
For Copper Sulfate Supplies: Wammock Farm Services Inc. www.wammocks.com
The Magic of Electro-Chemical Etching
Metal Salt etching is a new methodology which is fundamentally different from the aggressive chemistry of traditional acid etching, with its hazardous gas emissions and by-products. The new method is akin to creating a liquid battery. The etching battery consists of two types of metal that act as the charged poles of the battery - anode and cathode - and an electrolyte medium (here the salt solution) that transmits electric charge and allows metal ions to migrate. The process lacks none of the mystique of acid etching. The alchemical magic of seeing a solid metal vanish in a liquid is in many ways an even more tactile and engaging activity and produces startlingly good results.
The dissolved copper ions (from copper sulfate) create a powerful electric potential which literally pulls away the surface atoms of the silver-grey metal plates it comes into contact with. The more copper ions there are contained in the solution the greater the etching potential of the bath; therefore this process works best when used in a larger tray or tank which has a greater electric charge and can etch more metal for longer. The etching process produces various solid by-products; the metal oxides and hydroxides of the etched plate on the one hand, and a fine deposit of pure atomic copper on the other.
While a Saline Sulfate bath is active and usable it retains a green colour, although after a while the original translucent green is replaced by what looks like a much more unattractive soup of green sludge. But worry not: the sludgy looking bath etches just as well as a translucent one. Stir up and mix this sludge with a stick or a brush before each etching session. This re-dissolves the copper compounds that are crucial to building up electric charge for further etching.
Once the etching capacity of the bath does slow down, there are two options:
Recycling, Neutralization and Disposal
The process comes full circle. The very action that makes the Saline Sulfate Etch work so wonderfully as an etching bath - the depletion of copper ions - also facilitates its recycling. Concentrated copper ions are regarded as an aquatic pollutant and must not be allowed to get into waste water. As more and more copper ions react with the metal plate during etching these are converted into their inert cousins: solid copper atoms. If a sufficient quantity of metal is etched, eventually all copper ions are removed. A fully depleted bath is recognizable by two features: (i) the solution no longer corrodes metal and (ii) the solution is no longer green, it is clear.
Spent solution easily separates into a clear liquid and solid particles.
Prepare a spent etching bath for recycling as follows:
Although copper sulfate is a comparatively safe chemical for etching, it is considered a marine pollutant, and if present in rivers or lakes it can kill fish. It is crucial that solutions containing this salt are never poured down a drain without following the above instructions. Only a spent solution that is lacking the green coloration (which indicates the presence of copper ions) and that has been neutralized with sodium carbonate is safe to be discarded.
The Small Business section of your local Environmental Protection Agency offers free advice on the safe disposal of exhausted metal salts and liquid ferric-based etching solutions. Solid zinc, aluminum, steel and copper residues may be safe for local disposal once any copper sulfate content has been fully removed. Professional printmaking studios should utilize a commercial chemical disposal firm to pick up spent etching by-products. Visit your local EPA page for details of local firms. Visit www.epa.gov.
As a long time hazardous waste management professional, artists in the United States will have much better luck working with local governmental agencies than federal agencies like the EPA. A good way to find assistance with managing hazardous waste (like etchants) is by visiting www.earth911.com, typing the word "hazardous" in the search box, then entering one's zip code. If there's a local agency, it will probably be listed.
Next best? In a search engine, type the name of your city or state and the words hazardous waste and see which agencies (.gov) pops up.
Click for Nik Semenoff's update (2009) on copper sulfate based etching: The Complete Elimination of Metal Compounds from the Mordant before Disposal
Click for Nik Semenoff's Chemistry of Using Copper Sulfate Mordant
The Italian Printmaker Fabiola Mercan in recent years continued further tests with alternative recycling strategies for copper sulfate-based etching solutions, and also collaborated with Nik Semenoff on this topic
Fabiola Mercan also offers a Facebook group with extensive updated information on many aspects related to nontoxic printmaking,
click here to view:
Zea Mays Printmaking is a studio, workshop, gallery, educational facility
and research center dedicated to the safest and most sustainable printmaking practices available.
The studio frequently utilizes the Saline Sulfate etching method,
and researchers Tessa Chambers and Nick Osetek
published detailed findings on their work with copper sulfate-based etching on the
Zea Mays research web resources.
saline etch for aluminum refinement
A Guide to the Safe Use
of the Metal Salt Etching System
| METAL SALT ETCHING|
Copper and Brass: Etch in Edinburgh Etch
Zinc, Steel, Aluminum: Etch in Saline Sulfate Etch
DO NOT MIX WARM AND COLD COLORED SOLUTIONS AND METALS