Liquid Flux as Etching Resist for Basse-Taille

Phyllis Wallen described her technique for me more than twenty years ago. Phyllis died September 28, 2000. Her method of working is still current, and I am glad to be able to include it in this book. The liquid flux that Phyllis used as her etching resist was similar to the opalescent crackle Doris Hall used that predated the liquid flux.

Plate: 7" diameter, Copper, etched, bàsse-taille, enamel, Circa 1974
Plate: 7″ diameter, Copper, etched, bàsse-taille, enamel, Circa 1974

In bàsse-taille (bahs ty), the metal has a design or a texture partially cut into its surface before being completely covered with transparent enamels, which allows the design or texture to be seen. Engraving and etching are among the many methods for cutting the metal. A resist is first painted on the areas that are not to be etched before the metal piece is placed in an acid bath. Among the materials that can be used for the resist are Klyr-Koat liquid flux, Thompson’s medium fusing liquid flux and crackle. This description uses the Klyr-Koat liquid flux as the resist and nitric acid for the etching bath. After coating the metal with the liquid flux, the dried coat is sgraffitoed to expose the metal that will be etched. After the sgraffitoing the liquid flux coat is fired. This fired coat of enamel is the resist for the etching.

The liquid flux is applied by dipping a cleaned 18 ga copper plate or bowl in a shallow bowl with the liquid flux. The liquid flux is first tested with a spoon to determine whether it is the right consistency. You can tell by the way it coats the spoon. If the flux is too thick, distilled water is added one drop at a time. If it is too thin, then it has to be set aside until some of the water evaporates. Some of the binder will be lost if you spill out the excess water. The material needs to be stirred often while it is being used because it settles to the bottom of the container. With experience you will learn the right thickness for this base coat. If it is too thick, then when it dries you will not be able to draw any fine lines in it.

After you dip the copper piece in the liquid flux, shake off the excess into the container and place the piece upside down on a hammock or trivet until the coating on the front and the back dries. The dry, unfired liquid flux is very sensitive and will show every touch or water mark. If you make a mistake in your drawing, remove all of it and dip the piece again. Patches will show when the piece is fired. The design or texture to be etched is sgraffitoed with any kind of a pointed tool; the finer the point, the thinner the etched line will be.

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To prevent the dry liquid flux on the back of the piece from rubbing off while you draw on the front, place the piece on a slick surface, e.g., a piece of plastic or a shiny magazine cover. There will often be a thick accumulation of dried liquid flux around the face edge of the piece. This edge should be shaved down gently and gradually to almost the same thickness as the rest of the coat. You can use a 1/4″ dia dowel piece to thin down the dried liquid flux or any smooth tool. When the drawing is completed, the loose dry flux is tapped off and the piece is fired to maturity in the kiln at 1500°F. You will see your drawing in an oxidized line or pattern on the front and a layer of fired flux on the back when the piece is removed from the kiln. If there are any unwanted small pit marks in the flux, cover them with clear lacquer nail polish before placing the piece in the acid bath.

Make an etching bath solution of one part nitric acid to three parts water. Never pour water into the acid; always pour acid into the water to dilute the acid. Pour the water into a photographer’s rubber tray and then gently pour in the nitric acid. You can also put the bath in a Pyrex container and then place it on an electric warming tray set on low. The nitric solution etches faster when it is warm, but do not let the solution get hot or it will melt any lacquer or cause the enamel to move. A 6″ copper plate will etch in from 30 minutes to one hour. On a cold day in a cool solution, the etching can take two to three hours. Most writers say you get better etch with a slower etch, but Phyllis said she got a better line with a faster etch.

The depth of the cut in the metal, called the “bite” in etching, should be limited to one-third to one-half the thickness of the metal. Most enamelists use 14 ga to 16 ga for a deep bite and 18 ga for a shallow bite. Phyllis used 18 ga for her bàsse-taille plates and bowls.

When the etching process is complete, the piece is rinsed thoroughly, scrubbed with a brush under running water, and then dried. The oxidized lines are burnished with a glass fiber brush to brighten the copper so that they will be a golden flux color. For the first application of transparent, 80 mesh, leaded enamel, either Thompson’s #333 hard flux or #728 Amber is used. The enamel has been washed and dried. It is sifted on dry and pressed into the etched areas. Care must be taken to pack the enamel well along the ridges of the etched lines.

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If this first fired coat of the 80 mesh does not cover completely, the piece again is placed in the acid solution to remove the firescale and is rinsed well before another coat of that same transparent enamel is applied and fired. If the edge of the piece is ragged from being eaten away in the acid solution, it is ground or filed smooth at this point. Color transparents are applied and fired in thin layers; the firescale is removed from the edge of the piece between firings.

Generally, each coat is fired to maturity. The counter enamel is applied immediately after the first transparent firing on the front. If there are blemishes on the back, then the counter enamel needs to be a mixture of transparents and opaques to cover them. The counter enamel usually needs an additional coat as a last firing for the piece. Thick coats of transparent color may produce a cloudy final coat instead of the clear, brilliant transparent enamel that is desired. Make the last firing as fast and as high as you dare in order to add brilliancy to the transparent enamels. The edge of the piece is filed and then polished to a smooth finish to complete it.

Phyllis Wallen died September 28, 2000. She had been a noted enamelist in San Diego since the early 1970s. She was involved in the beginnings of the San Diego Enamel Guild.

By Lilyan Bachrach - Copyright © Lilyan Bachrach 2004
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Excerpts from the book: Enameling with Professionals
A unique book for everyone interested in the art and techniques of enameling
ISBN 0 9719252 0 8
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