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  • Writer's pictureChiara

Caustic Soda Etch

I first became aware of the etched lino technique through Laura Boswell’s work, which I came across in the Linocut Friends Facebook group. The organic textures produced through the chemical erosion of the surface of the block significantly enhance her landscapes. Thinking about the skin textures in my working drawing reminded me of this technique. The approach to mark making relies on exposed lino being etched away by a Caustic Soda solution, leaving protected areas of the lino in relief. Wax, bitumen or acrylic resists can be used to protect the lino. Imperfections and weaknesses in the resist leave the raised surface of the block partly eaten away producing the characteristic rough textures. Since it is at best a rather uncontrolled process, I did some experimenting before committing to it. I also introduced a second block of lino, rather than risking the reduction block on which all my future layers depend.

An internet search brought up this blog entry—and Laura Boswell’s comment suggesting that’s where she started from too. *language warning*: this post contains strong language commensurate with the strength of the chemical reaction! My lecturer also suggested the description in The Printmaking Bible (and thereby added one more book to my Christmas wish list). Health and Safety considerations meant using appropriate Personal Protective Equipment and working at home, rather than in the University Studio, since the use of Caustic Soda there would require a specific Risk Assessment, which couldn't be done in the time available.

I experimented with L’ascaux acrylic resist and the stop out ground (bitumen and turpentine) used in the RMIT studio for copper etching. The stop out ground seemed to resist the caustic soda more effectively and also promised to be easier to wash off the surface of the block after etching, so I settled on that. In addition to sanding the surface of the lino to prevent the caustic soda solution from sliding off the block, I thickened the solution with a 5 ml of wheaten cornflour per 250 ml of water. I added 40 ml of caustic soda crystals to this mixture. When it had thickened and cooled I painted the solution on to the prepared lino. I reapplied the mixture after an hour and then left the block overnight. The next morning it was time to rinse it well, neutralise the caustic soda with vinegar and rinse again.

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