Mordants or Acid Baths

Chemical flasks for mordant webpage


I have provided a few general recepies that are used around our shop. Caution should be exercised when using caustic, toxic, or flammable chemicals. Many of these formulas can be found from the the old etcher's handbook "The Art of Etching," by E.S. Lumsden.


Ferric Chloride:
This etchant is usually used to etch copper plates and is safer than most printmaking acids. It is actually is not an acid, but rather a corrosive salt. It can be purchased in gallon plastic bottles and used directly, without any dilutions with water. You can test its strength by using a hygrometer, which should read 42 baume. Copper plates are etched in vertical plastic tanks. No noticable fumes are created with a copper etch, but one should be cautioned that etching zinc will produce fumes and may create unpredictable problems for using the same bath to etch copper after the zinc.

Edinburgh Etch:
This formula was obtained from Warring AH Printmakers Studio

  • 4 liters of ferric chloride solution
  • 1 liter hot water mixed
  • 300ml citric acid powder (ratio of 3:1)

Keith Howard is attributed as being the inventer of this etch. He experimented with ways of combining non-toxic substances to make a faster and cleaner etch. His key ingredient was citric acid. When mixing this acid at the proper proportions with ferric chloride solution, one could accelerate the reaction time and increase the precision of the bite. A scientific explanation is that the reaction frees ferric atoms from the weaker water molecule.

The Edinbergh etch could also be used to etch zinc, brass, and mild steel, in addition to copper. The reaction minimizes sediment production, allowing for a cleaner etch. Apparently, the citric acid is chemically able to keep the metal salts dissolved, instead of forming as the usual dark precipitate on the plate surface. This allows the etch to give sharper detail. Howard states that citric acid powder also has the benefits of being non-toxic, but still requires the use of dust mask and goggles to prevent absorbing the fine powder.

Bordeaux Etch for Aluminum or Zinc:
The recipe is from Nik Semenoff's research: (increasing salt will allow more effective results with both aluminum and zinc)

  • CuSO4 (copper sulfate -- bluestone) 1 kilogram
  • NaCl (sodium chloride -- table salt) 250 grams
  • NaHSO4 (sodium bisulfate -- Sani Flush ) 25 grams
  • H20 (water) - depending on bath strength 10-20 liters

Using copper sulfate to etch zinc was adopted by contemporary, Cedric Green, who coined the name, Bordeaux etch, and was used as early as the late19th century by Spanish printmakers. Nik Semenoff has successfully researched how this chemical could effectively etch Zinc. This is done with the additon of common table salt. I have not tested his results, but have linked to his research here: Bordeaux Etch.

Semenoff states that the etch has a pH of 2.5 - 4.5 and will not react harmfully with skin tissue or have corrosive effects on clothing. As the plate is etched, the copper sulfate is eliminated, leaving harmless chemicals that can be safely discarded. Copper within the bath can be recycled, so there is no problem with copper waste.

Nitric Acid:
(We no longer use Nitric Acid in our shop, because of it's toxic fumes and potential for severe skin burns or ignition.) I have provided links, if you wish to pursue this further: Artisan's Lane etching instructions

Etching Zinc Plates:

  • (1 part) 70% nitric acid
  • (11 parts) water

This gives a fairly controlled etch. Etchant is placed in flat tray, under ventilated acid hood. Acid bubbles must be dispersed with feather, while etching.

Dutch Mordant:
crossbones skull poison symbol(We no longer use Dutch Mordant in our shop, because of it's toxic fumes and potential for severe skin burns or ignition. Dutch Mordant is primarily used to etch copper in a flat tray. Feathering away bubbles is not required as it gives a very clean etch and little under-biting of lines and textures. I have provided links, if you wish to do your own research.)Chicago Artist's Resource Dutch Mordant Hazards

"The Art of Etching," by E.S. Lumsden lists a formula called Smille's Bath. It was first presented in Lalanne's Treatise of 1880. The chemicals in this mixture are extremely dangerous and must be mixed under acid hood, with lots of body and eye protection.

  • (5 oz.) Water
  • (1 oz.) Hydrochloric Acid
  • (1/5 oz.) Potassium Chlorate

Another variation of this mixture is called "The Dutch Bath," or otherwise known as the traditional Dutch Mordant. It consists of

  • (880 grams) of Water
  • (100 grams) of pure Hydrochloric Acid
  • (20 grams) of Potassium Chlorate

Here is a link to health concerns of the artist: Additional Warnings




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