"January in Jeffersonville, Vermont" oil on copper. sold.
These passages are right out of the book, "Copper As Canvas" by Phoenix Museum of Art. Chapter four by Isabel Horovitz.
Preparation of the Support Prior To Painting
Many painters also were engravers and etchers, and it seems reasonable to assume that they would have been familar with the tools and materials for plate polishing and cleaning. However, painters must have been concerned about the potential problems of adhesion between the support and the paint, and were aware that copper plates required special preparation prior to painting. Probably the most important requirement was that the copper sheen had to be roughened to provide tooth for the application of the paint. Almost all paintings on copper appear to ahve a roughened surface to a greater or lesser degree, which when carried out, would remove the layer of red cuprous oxide, cuprite (Cu20), formed by a reaction between the surface of the copper and oxygen in the air, and would increase the surface area available for bonding, to accept the paint. Under magnification, the roughened surface area of the metal is perfectly described by the early microscopist Robert Hooke, who notes the parts of a razor that had been finished on a grinding stone "looking almost like a plow'd field with many parallels, ridges, and furrows, and a cloddy, as 'twere, or an uneven surface."
Occasionally the surface may sinply have been scored at intervals, sometimes resulting in poorer adhesion of the paint.
Artists' manuals and treatises offer information on the preparation of copper plates and evidence of the methods described can be seen in paintings. Although the practice of painting on copper is often mentioned in conjunction with the use of other supports, it is in preparatory layers that some variations in practice and materials can be found. After the surface had been roughened, it was usual to apply one or more preparatory layers, prior to painting, as for paintings on panel or canvas. But artist using copper plates seem to dispense with an initial glue size and chalk ground layer, having no need to islolate the wood or canvas fibers from the oil, or to fill interstices of textured fabric or panel grain. In general, written sources imply that the preparation of copper plates was relatively simple which perhaps indicates that artists would prepare the plates themselves rather than buy them ready-grounded.
Some advice was offered by the Spanish artist Francisco Pacheco (1564-1654) in the year 1649 "metal plates, being smooth and clean, are primed only with one very thin layer of white lead and umber in oil which is put on and spread with the fingers and not the brush."
Another Spaniard, Palomino, gives more detailed instruction, writing in 1715-25. "Metal plates are prepared in the same way was the panels but to achieve smoothness and polish in the preparation, a priming color of white, umber, and a little red earth must be made and reground very well. Plates should always be rubbed first with garlic because they tend to have some slight concavities in which the imprimacion is slow to dry. After the color is well spread on with the brocha or pincel (brush) it must be evened by pressing and rubbing with the ball of the thumb (if the plate is small) and with the heel of the palm if it is large. The preparation is blended by alternatively rubbing on or removing imprimacion all over the surface until it remains even everywhere.
Then, either with a soft, bland pincel, or better with the tail feather of a dove...pass the tips of the hairs softly over the metal plate to leave the surface very polished and even."
There are numerous points in this passage that deserve attention. Clearly the choice of metal is related to a desire for "smoothnes and polish". Note the advice on the need to regrind the pigments, which might have appeared coarse and poorly bound within the medium when applied to highly smooth surface. The reference to "concavities" may refer to the localized dips in plane created by hammering. Slowness in drying in the concavities, where the film might be thicker, may have encouraged artists to restrict themselves to thin films. Whether garlic would speed up the drying process is not known, but it would have given some tooth to accept the paint film. Rubbing a sheet of copper with a cut clove of garlic 9or strained garlic juice for a smoother film) wets the surface and provides a sticky, mildly grainy base over which a thin film of paint is easy to control.
In a French manual of 1773, Watin raises a related point concerning wetting, an important factor for adhesion: "If you paint on copper, iron, or other pure materials...which are highly polished...which do not easily accept a paint film: which make paint glide over them, one must put a little turpentine in the first layers which helps the oil to penetrate."
The application of the priming with the thumb or palm is especially interesting, as finger or palm-prints have been observed in this layer on a number of paintings. It is also mentioned in a French treatise by Pernety, in 1757: "...one primes copper sheets with a layer of oil painting, which serves as a base for working. One gives it two or three of these layers, and when the last one is still tacky, one rubs it everywhere with the palm of the huand to give a tooth (grain) that accepts paint more readily." Applied like this in very thin layers, a smoother finish may well have been achieved than by brush, and which thin paints would not have spread so evenly and often results in a more regularly streaked appearance. Examples of fingerprints in priming layers have been noted in northern and southern paintings, ranging over different periods. In Cavalier d'Arpino's painting, "Archangel Michael, finger- or palm-prints are evident in many areas where the uppermost layers of paint are their thinnest.
Despite the attention to smooth finish, generally the written sources emphasize the relative ease of preparation. The English writer, Robert Dossie, in his Handmaid to the Arts, 1758, states, "When copper plates are used, there is no occasion for any other priming than one coat of oil, and lead, or oker, rendered of the colour desired..."
The near-pristine state of many copper paintings can give valuable information on the artist's technique, but it is percisely this state combined with the usually small size of these paintings that instinctively limits invasive methods of investigation. Although few examples have been analyzed, the materials seem broadly consistent with those mentioned in written sources and are often similar to those used in the upper preparatory layers on other supports.
Most paintings on copper appear to ahve a thin, pale-toned preparatory layer between the paint film and the copper support. In almost all paintings examined, this layer covers the copper completely, but the metallic nature of the support is evident. In some paintings it is very hard to see whether there is a ground or imprimatura layer, and the layer structure can only be examined by taking a microscopic sample and examining it in cross section. Even when the red glow of copper is visible, a ground layer may be present as in Von Aachen's "Entombment". In "Rest on the Flight into Egypt:, attributed to Domenichino, for example (examined at the Courtauld Institute of Art in 1981), the cross section shows how the smoothly and thinly applied ground layers echo the flatness of the support. The initial layers consists of lead white and earth pigments over the copper; the layer above represents either a second priming or underpaint for the sky and contains a slightly higher proportion of earth pigments.
The paint for the preparatory and paint layers consisted of pigments ground in oil. There has been very little investigation of media used in painting on copper during the period from the sixteenth to the eighteenth centuries, but analysis carried out so far suggests that linseed oil was used. In contact with copper, linseed and other drying oils used by artist turn green due to a reaction between the copper in the plate and the fatty acids in the oil. Beneath the ground layer of most paintings on copper where cross section have been examined, a green transparent layer can be seen. It is extremely thin, typically between 2-8 microns, and its color does not affect the appearance of the painting. Its effects are uncertain, particularly concerning adhesion, but it is a common feature of the layer struction of paintings on copper, whether in good or poor condition. It is not clear if oil was applied deliberately as a separate layer or whether it was formed coincidentally by the prolonged contact of the paint medium with the copper. Reactions could also occur as a result of contamination from materials used to clean the plate, particularly as methods and mixtures borrowed from etching and engraving practices might have been employed. The use of garlic in preparing the plate is difficult to investigate, since its active components are volatile, but in contact over time with copper, its juice can also result in a transparent green film.
There appear to be very few paintings where a ground or thin preparatory layers has not been used, althugh De Piles suggests "for copper, there is no other preparation to make other than to cut a clove of garlic in to and to rub it on the side of the plate on which you wish to paint, unless you wish to have a color other than the copper itself."
There is no suggestion that the reflectance of metal could be used to enhance the image, by enriching or adding brilliance to the tone. De Lairesse, for example, in his discussion of colored backgrounds to flower painting, uses metals to denote color and "luster' rather than actual metallic reflectance. Yet any idea of a deliberate desire to hide the natural state of the support does not seem relevant, given the contemporary interest in the effects of supports such as marble, jasper, and porphyry, where the veining was used as an integral part of the composition. In Rottenhammer's "Coronation of the Virgin" (The National Gallery, London) although there is gray underpainting in certain parts, there are also many areas where the outlines of the forms have been brushed directly on the copper. The copper itself is allowed to show through, particularly in the gray clouds, which are very thinly smeared by his fingers with opaque paint. The effect is a warm, glowing tone, that gives depth to the clouds on which so many figures are resting.
Tomorrow I will type up the section entitled "Examination of Working Method" in chapter four by Isabel Horovitz.
I never use any medium while I am painting. I like to keep things simple. I also never use garlic either. I couldn't handle the garlic smell on my fingers while I was painting all day! I do sand down the copper panel and start to paint directly.
Daisy and Duke are tired from swimming at the beach! Daisy just loves to sneak up on seagulls floating around on the water. She gets very close! Have a great night. Get out and paint!
