Ferric Chloride Etching Solution
These notes are based on a Non-Toxic Printmaking Workshop that was provided by Elizabeth Dove in July of 1998 at the University of South Dakota, Vermillion.
Annie Gregg etching a copper plate in ferric chloride/Edinburgh etch solution. Using a needle tool she has drawn through a dried hard ground coating of Future Acrylic Floor Coating Solution and has bitten the exposed line work for 10 minutes. Contact paper protects the back of the roofing copper plate and a folded length of wide plastic tape is adherred to the plate's back as means of suspending the plate in and moving the plate to and from the etching solution.

A.  General Ferric Chloride Information

1.  Produces a precise bite as a slow etchant.

a.  An aquarium aerator pump circulates the solution and facilitates faster biting.

2.  Ferric Chloride solution lasts between one and two years

3.  Ferric Chloride works on copper, zinc, stainless steel, but be sure to use only one type of metal in a tank of ferric chloride in order to keep the solution active and prevent dangerous chemical reactions from occurring.

4.  "Sacrificing" a clean, metal scrap (in this case a bent scrap of copper) will activate a fresh tank of ferric chloride solution.

5.  A range between 42° to 45° Baume solution is best and for a routine hard ground etch it will take from 60 to 90 minutes.

a.  A hydrometer is used to measure the density of the solution.

b.  At 48° Baume add water to reduce the density of the solution and stir for distribution.

1)  As the solution nears 50° Baume it is difficult to gauge the biting of the plate as the solution becomes grease like.

c.  Don't use a solution measuring 35° Baume or lower since the high ratio of water to ferric chloride with detrimentally affect acrylic bases (screen filler, acrylic aquatint).

1)  Leave the cover off of the tank and allow excess water to evaporate and so increase the solution's Baume reading.

B.  Plate Preparation

1. Back the plate with contact paper cut to the same size as the plate - it can stay on during proof printing.

a.  Can also coat the plate with "Future Acrylic Floor Base" and then coat with contact paper.  A mixture of 10% ammonia and 90% water will strip the Future from the plate.

b.  Layer the back of the plate with acrylic packing tape; this must be removed before proofing the plate.

2. Packing tape is used to make a hanger for the plate.  It is from the length of tape that the plate is suspended in the vertical tray.

a.  Use about a 14" length of tape and be sure to fold it back on itself so it doesn't stick to anything else in the tank.

b.  Use a permanent marker to write your name on the tape for identification.

3. Etch a test plate to establish times for gray scale and line widths.  Perhaps begin with 2 - 3 minute intervals.

a.  A test plate for determining etching times can be made by painting out strips with acrylic screen filler that is dried completely with a hair dryer before submerging in etchant.

b.  Using a metal-less clothes pin, pinch the top of the folded tape length over and to the vertical tank top edge.

4. When finished with a timed etching session, remove the plate and thoroughly rinse both sides of the plate and tape with water.

5. Rinse plates completely after session in ferric chloride.  Take care not to get on clothing since it makes evident and permanent stains on materials and eventually skin if left on for a long enough period.

a.  Rinse eyes thoroughly should it get in your eyes.

6. If any material is to be applied and/or attached to the plate, it must be deoxidized.

a.  Mix ½ cup of salt to one gallon of white vinegar.

b.  Submerge the plate in a tray with enough of the vinegar solution to cover it completely.

c.  This is not necessary for printing or stripping the plate.

7. Use an alkali solution such as caustic soda or an ammonia solution to remove screen filler from the plate.

8.  Sodium Carbonate (soda ash) neutralizes ferric chloride.

9.  Don't suspend plates by their tape tails using devices having any metal in them.  Use only plastic or all wood clothespins.