Research into a Safer Mordant for Copper Plates

I have been testing my new mordant for copper plates and here are some results. I have gone through the usual line work using Ferstmans’ hard/soft ground that is on my university website. That all worked fine, but the true test is the use of toner washes that print as a positive, just as drawn on the plate. At one time I used diluted shellac until I was shown the hard ground made from Graphic Chemical Ink Co; developed by Gerald Ferstman at the university in Lexington, Kentucky. It is a waterbased relief ink that uses emulsified shellac as the binder, so reacts to heat in much the same way as diluted shellac.

Cu toner wash B Cu toner wash A The toner wash is applied in a thinner manner than for waterless litho because the darker areas will print solid color from the aquatint effect of wiping the plate. The toner is set with heat to make sure it is bonded very well to the plate, then cooled. The ink is modified with a bit of softer plastic material as shellac become brittle when dried with heat in this technique. The ink is rolled out on a slab into a very thin film, which is easy to judge by the color intensity, then applied with firm pressure over the toner image to make sure the ink contacts the metal between the particles of toner. Roll the ink on from many directions to make sure all areas are covered, but do not build up a thick layer of ink, especially in the image area.

To harden the ink, I use a propane camp stove as I do not have a hot plate, but even most of these are not quite hot enough to change the shellac into a horn-like surface that will stand up to any mordant. The ink has to get above 150 degree centigrade for this effect to take place.

After the plate cools, I take turpentine and short stubby brush and start to dissolve the toner through the shellac film. At one time I used a coarse stencil brush, but found a short softer one used to apply facial makeup, which seems to work better. Take your time and gently washout the toner image, leaving bare metal for the mordant to attack.

While a tray bath works well, I have found that bubbling air through the mordant speeds up etching, but I devised a system so that there is a more gently flow of mordant against the image, producing a more even tints across the entire plate. The plate was etched for about 30 minutes in my first test, but I found that was not enough after pulling a proof. To get a better bite, I cleaned the plate and when I was doing more research, I applied a very thin film of the waterbased ink as before, making sure the depressions were not filled with ink. This plate was re-etched to produce a darker image. Compare the two image above.

For another test, I repeated the toner wash on a new copper plate and etched it for about 45 minutes. This is not an accurate test as I had modified the mordant a number of times between the above plates and this one, so activity would certainly be different. Such things as specific gravity and pH are a factor that were not always recorded or taken into account.

Cu toner wash C This was an old piece of common copper in my workshop, which had seen better days, so it was hard to remove the blemishes and scratches on the surface. While the dark area looks fine, this plate could be improved by using the rolled on ground again to etch the left side image, but block out the dark image after the ink had been hardened with heat. Future floor polish works fine as a blockout.

The hard ground it removed from the plate with sodium metasilicate in most cases, but the ink could be hardened enough with high heat that it doesn’t want to come off easily. For copper you could use a strong chemical such as sodium hydroxide and let the plate sit in a solution for some time. In very severe cases, I have had to place a facial tissue on the plate, wet it with lacquer thinner, then place another plate about the same size on top to prevent fast evaporation. That has always done the job.

The ink I used was Daniel Smith #7 Standard Black Etching that was modified with their waterbased relief ink to soften it; instead of using Easy-Wipe. On drying, the proofs are completely waterproof as with regular ink. The nice thing about this feature is that the plate is washed out with sodium metasilicate or a commercial waterbased grease remover. No solvent is required for any reason. I also use Tulle fabric, instead of expensive Tarlatan, which can be washed out with soap and water after a printing session.

So what is the mordant formula? Keep in touch as I will disclose it and other mordants I have been working on for aluminium and zinc – after I submit it to be published it in a journal in the near future.

By-the-way, this toner wash technique works well on zinc and aluminium with my copper sulfate mordant; as well as on copper plates with your favourite etching bath.

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