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Transparency or Opacity

(Excerpts from ART HARDWARE: The Definitive Guide to Artistsí Materials, by Steven Saitzyk © 1987 revised 1998)

Since the average painter consumes as much white paint as all the colors in their palette combined, the issue of transparency is pretty opaque.  White is opaque and will impart that characteristic to all colors that are not already opaque.  If you are not the average painter, and use little or no white, glaze your colors, or are looking for subtlety, the relative transparency of the pigments you use becomes vital knowledge.

Each pigment used in oil paint, by its own chemical nature, will tend to be either transparent, semitransparent, semi-opaque or opaque.  Most blacks, blues, violets, and purples are transparent, as are colors where the pigment is a like a dye‑pigment, such as alizarin crimson and madder.  Earth colors range from semitransparent to semi-opaque, depending on their source.  All cadmium and chrome colors, all whites, or colors that are made with white (such as Naples yellow and flesh tint), and genuine vermilion are opaque.

Of all the whites, zinc white is most transparent, followed by lead white and then titanium white, the most opaque.  You can make a transparent color semi-opaque or opaque by the amount of white you add to it.  Many colors can be made nearly opaque with as little as 10 percent white without any appreciable change in the surface color.  Opaque colors can often be made semitransparent by thinning them with a painting medium and applying in thin glazes.

Virtually all manufacturers' color charts are encoded with information regard≠ing the transparency and opacity of the colors in their unmixed state.  Some companies even label their paint tubes.  It is important to note that in lesser grades of paint, it is more common to have expensive colors replaced with blends of other less costly colors, which in turn can affect the transparency and opacity.  A mixture of white and phthalocyanine blue, for example, is commonly sold as cobalt blue hue and regrettably sometimes sold as cobalt blue.  This blend is opaque and does not produce the same kinds of tints when mixed with other colors. Genuine cobalt blue is prized for its transparency as well the delicate tints it can produce, as is said to radiate its color in the presence of natural light.  Another example is cadmium red, the better grades of which are made from C.P.  cadmium sulfo‑selenide, and which is prized for its opacity and brilliance.  It is sometimes replaced with lesser grades, which are often mixed with barium sulfate, or replaced entirely with Azo pigments and are therefore less opaque and not as bril≠liant.

It used to be common practice simply to paint over undesirable areas with opaque colors until it was discovered, after many years of aging, that areas which were hidden began to show through the increasingly transparent surface.  This phenomenon is called pentimento.  Therefore, if an area needs to be repainted, the area should first be prepared with a new ground of white paint.

To an artist who paints very large, these differences may seem insignificant for, if one has to stand twenty to thirty feet back from the surface of the painting to see it, it is unlikely that small details will be noticed.  However, if you are a master at the craft of painting, or paint in a style where details must and will be seen, these differences are very important.

(Excerpts from ART HARDWARE: The Definitive Guide to Artistsí Materials, by Steven Saitzyk © 1987 revised 1998)



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