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| Ferric Chloride: |
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| 1. |
Ferric chloride has virtually replaced the use of nitric acid and Dutch mordant as a solution for etching copper. Although etching is commonly considered a process of using acid to bite the metal, ferric chloride is actually a corrosive salt. Ferric chloride has the advantage of greatly improving the safety of etching. Ferric chloride is free from harmful gas emissions, it will stain but will not burn skin. |
| 2. |
Ferric chloride is available from most chemical suppliers in the less saturated 42 baume. The most reliable source for 48 Be ferric chloride, commonly used for photogravure, is FUJIFILM Hunt Chemicals Specialty Products Group. A hygrometer is used to measure the baume of the ferric chloride. If ordering an already dilute, 42 Be solution, there is no need to adjust the solution with the addition of water. |
| 3. |
A ferric chloride etching bath is most effective after a bit of etching has taken place. There are a few visual cues that assist in determining the efficiency of a ferric bath. When new, ferric chloride is a clear red/brown color. As copper plates are etched, the solution is a muddy brown, and remains quite effective. Once the solution turns a dark greeish black, the bath is usually slow, and may need to be disposed neutralized and disposed of safely. (It is the addition of the copper in the ferric chloride bath that is cause for hazardous disposal). |
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| Etching Times: |
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| 1. |
There is not an exact chart to prescribe the exact length of time a plate should be left in the acid. Several considerations come in to play when determining the length of time one should expose the plate to the etchant. Higher temperature speeds up the action of the etchant. The strength (baume) of the ferric chloride, and the amount of use the solution has had impact the speed of the etch. The best way to determine the effect of an etchant on the plate is by experimentation and observation. |
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| 2. |
It is advisable to etch a small test plate to determine the strength of the bath and the effect time has on the exposed plate. I recommend a test plate where you double the exposure time with each period in the bath. Begin with 1 minute, then 2 minutes, then 4 minutes, 8 minutes, 16, minutes, 32 minutes, 64 minutes, and even 128 minutes. This test plate will provide you with a great deal of information quite quickly, and assist you in making decisions about how the ferric chloride bath effects the weight of the etched line prior to getting involved with a large plate. |
| 3. |
The longer the plate is immersed in the bath, the deeper the line is etched. The deeper the line, the more ink it holds. To achieve varying tonal effects, vary the length of time the inscribed line is exposed to the etching solution. Samples: shallow etch, medium etch, long etch. |
| TIP: |
Maintaining a notebook/log of etching procedures and experiments will help you process and repeat information. |
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| Etching Procedure: |
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| 1. |
The back of the plate must be covered with an acid resist prior to etching. If the plate is not going to be heated, as when melting rosin or applying softground, contact paper is a simple solution. Spray paint is commonly used if the plate will be exposed to heat. |
| 2. |
Firmly adhere several pieces of masking tape to the back of the plate prior to immersing your plate in the vertical Ferric Chloride tank. The masking tape functions as a handle for lowering the plate into the bath. Burnish the tape well to assure good adhesion to the plate. |
| 3. |
Lower the plate into the etching bath until the top edge is fully immersed. |
| 4. |
Use clothes pins in the bin near the bath to affix the tapes to the side of the bath. |
| 5. |
Periodically check on the plate while etching. |
| 6. |
When removing the plate from the etching bath, remove the clothes pins, lift the plate directly above the bath, lower one corner, and let the ferric chloride drip back into the bath. Do not let solution drip on the counter or on yourself. |
| 7. |
When finished etching the plate, thoroughly rinse both front and back under cool running water. Mop up any ferric chloride (or copper sulphate) spills with sodium carbonate and water. |
| TIP: |
You may insert a sharp point into the etched line to feel the depth of the etch, or better yet, wash out a 1/4 inch area of the plate. turning the plate against the light will permit you to see how deeply the line is etched. do not wash off the ground until you are certain the plate has been etched sufficiently. If additional etching is necessary, retouch the washed out spot with ground, let it dry, redraw the area, and place the plate back in the ferric chloride solution. |
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| NOTE: |
Please be mindful of the communal nature of the VCU printmaking studios. Conduct a quick glance through the studio at the end of your work period. Return tools proper storage areas, clean off work tables and ink stands, and dispose of any soiled paper towels and newspaper. |
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