Painting on Copper

Historical Use and Preparation

While we do not know why oil painting on copper enjoyed popularity from the sixteenth to eighteenth centuries, we may be able to provide some reasons based on historical evidence linked to artistic tradition in both the cultural and economic context of the period.

Concerning artistic tradition, paintings on copper may have arisen out of the practice of applying transparent oil glazes to metal sheets [1,2], but the progress in the fifteenth century of enameling on copper or bronze may have influenced its development, due to its widespread popularity [2].

The earliest literary evidence of oil glazes on metal is found in the eighth century Lucca Manuscript, where a recipe describes how to make a glaze of oil and resin to be applied over tin foil, in a technique known as ‘Pictura translucida’. These glazes were colored yellow to give tin the appearance of gold leaf [1,2]—a kind of imitation gold. These stains were also used on different metals to imitate gilding as recorded in later sources [2].

With the invention of printing, engraving and etching became widely popular in Europe during the fifteenth and sixteenth centuries. This meant that copper plates were readily available to painters, some of whom were also etchers and engravers [1].

Economic factors may have also led to the rise in popularity of copper as a painting support. Readily available copper plates meant that prices were affordable to artists [3]. Jørgen Wadum’s study of Antwerp coppersmiths, and the relative costs of panels, artists’ materials and paintings on copper revealed that prices for copper plates were roughly similar to those for oak panels of comparable size [4].

An ‘appreciation for the precious and the remarkable, the rare and unusual, the refined and exquisite’ developed among wealthy patrons in sixteenth-century Europe, which is reflected in cabinets of curiosities. This lead to the proliferation of different supports for painting, such as ‘alabaster, amethyst, lapis lazuli, marble, quartz, slate…’ and, of course, metal. It is logical that paintings on copper would also be seen as ‘rare and precious’ objects in art collections of that period [3].

The gradual waning of oil paintings on copper from the latter half of the seventeenth century in Italy and the Netherlands is even less understood than their appearance. On the other hand, countries such as France and Spain continued to admire this kind of artwork throughout the eighteenth century, and many of their artists chose copper as a support for their paintings [3].

Attraction of Copper Supports

Copper supports were attractive to artists for both practical and aesthetic reasons. Paintings on copper do not suffer from the same types of degradation causes as is the case for paintings on canvas or wood. They are not susceptible to biological degradation, such as mold. Supports from metal do not tear, puncture or crack as do canvas and wood supports. Since copper supports are rigid, they do not respond significantly to environmental variations of temperature and relative humidity. In normal indoor conditions, copper supports exhibit only minor dimensional changes due to temperature. The dimensional changes of copper are also similar to that of oil paint, as the temperature increases or decreases both expand and contract together. These properties of copper account for the surprisingly good state of preservation that some paintings exhibit today [3].

The portability of copper supports, which were usually quite small, also provided opportunities for artists to collaborate on the same painting even when they were residing in two different geographical locations [3].

Preparing copper plates for oil paint is easy, usually only consisting of a single layer of priming. The very smooth surfaces also provide an ideal substrate for rendering fine detail, which was especially popular in the style of paintings of that period. The non-absorbent surface of metal allows the application of thin paint layers that often do not ‘sink in’, a problem among oil painters even to this day.

Perhaps the most attractive reason among painters for using copper as a support for oil painting is the gleam of its metallic surface. The combination of copper’s smooth, non-absorbent surface, allowing the application of thin paint layers, result in paintings with a very unique, luminous appearance that many describe as ‘jewel-like’ [3].

Preparation of Copper for Painting

Although preparing copper plates for oil painting is simple, it requires some special attention so that paint layers achieve good adhesion. In historical instructions for the preparation of copper, this began with roughening the copper surface to ‘provide a tooth for the application of the paint’ [2]. This mechanical action not only removes any corrosion present from the surface, such as black or brown cuprite (CuO₂), it provides greater surface area for the effective bonding of paint to the metal. Historical treatises and manuscripts on this subject provide a number of different recommendations that include rubbing the surface with wood ashes and pumice stone [5].

The same treatises also recommend rubbing a garlic clove onto the copper surface or coating it with strained garlic juice [1]. The tacky coating of garlic juice can provide some ‘tooth’ for paint, but also gives the artist better control of the paint by providing drag for brush application of paint.

Some sources recommended applying turpentine instead of garlic to the copper plate to improve the wettability of the slippery copper surface, thereby enhancing adhesion of the oil paint.

Applying a layer of linseed oil to the copper surface is also mentioned in a few historical sources. This may have been a practice borrowed from etchers, because it was thought to improve the application of the preparation layers.

Priming Copper for Painting

Researchers have found a priming layer on the majority of oil paintings on copper studied. These primings contained lead white, white ash, black carbon, umber, yellow and red ocher and vermilion ground in oil. Historical sources mentioned that the grounds were to be applied by the palm of the hand, with the fingertips or by brushing, the first one being the most frequently referred in the sources [5, 6].

Bibliography

1. Isabel Horovitz. 1999. “The materials and techniques of European paintings on copper supports”. In: M. Komanecky, ed. Copper as Canvas: Two Centuries of Masterpiece Paintings on Copper, 1575–1775. Phoenix Art Museum. New York: Oxford University Press, pp. 63–92.
2. J.A. van de Graaf. 1976. “Development of Oil Paint and the Use of Metal Plates as a Support”. In: N. S. Bromelle & P. Smith, eds. Conservation and Restoration of Pictorial Art. London: Butterworth-Heinemann Limited, pp. 48–51.
3. E. Peters Bowron 1999. “A brief history of European oil paintings on copper, 1560–1775”. In: M. Komanecky, ed. Copper as Canvas: Two Centuries of Masterpiece Paintings on Copper, 1575–1775. Phoenix Art Museum. New York: Oxford University Press, pp. 9–30.
4. Jørgen Wadum. 1999. “Antwerp Copper Plates”. In: M. Komanecky, ed. Copper as Canvas: Two Centuries of Masterpiece Paintings on Copper, 1575–1775. Phoenix Art Museum. New York: Oxford University Press, pp. 93–116.
5. Isabel Horovitz. 1986. “Paintings on copper supports: techniques, deterioration, and conservation”. In The Conservator, 10: 44–8.
6. D. Vega. 2015. Study of the Ground Layer in Oil Paintings on Copper. Student’s project supervised by Dr. Leslie Carlyle and co-supervised by Dr. Isabel Pombo, DCR, FCT-UNL.