Natural (lapis lazuli) ultramarine (note 6) is the predominant blue pigment-one might almost say the predominant pigment-in the picture. It occurs mixed with varying proportions of lead white in the sky, the bluer passages of the more distant landscape, the lights and middle tones of blue drapery, the iris and the columbine flowers. Used pure, i.e. unmixed with white, it is found in the very dark shadows of Ariadne's blue cloak and the drapery of the Bacchante with the cymbals. Unfortunately when used alone in oil medium, ultramarine dries slowly and if applied in a thick layer, as in these shadowed areas, rather than as a thin final glaze, the top surface dries out first, shrinks and splits forming a network of unsightly broad shallow cracks. The effect is less noticeable now than before cleaning because previously the cracks were filled with deposits of old varnish, dirt and glue. They are clearly visible in the infra-red photographs (Fig.3) taken before cleaning, because the high reflectivity of the ultramarine for infra-red radiation causes the paint to appear almost white while the dirt-filled cracks are in strong contrast. When lead white is mixed with the ultramarine it assists drying and prevents this defect. Ultramarine is also the blue component in a mixture with lead white and a little red lake pigment, of the delicate mauve drapery of the Bacchante with the tambourine (Plate 3, p.29 and Plate 6d, p.47). The ultramarine in the ‘Bacchus and Ariadne’ is of the most intense colour and high purity of any so far met with. In the mid- and light blue areas of sky and drapery it is likely to be little changed, but in the very dark shadows mentioned may have become darker and duller in colour because of the combination of its very low refractive index (c.1.5) with the increase in refractive index and possible yellowing of the oil medium with age. A few tiny particles of a paler ultramarine (perhaps ultramarine ash, the last residue of the extraction process) occurred in the shadows of Ariadne's flesh (Plate 6a, p.47). It would be interesting to know if the lavish display of the most expensive of all pigments and of the highest quality was due to Titian's own enterprise or Alfonso's directions and whether its cost formed a separate item of payment.
Azurite (basic copper carbonate, 2CuCO3.Cu(OH)2) occurs as the blue of the sea and of the slightly more greenish areas of the distant landscape, giving a very subtle contrast to the faintly purplish hue of ultramarine. From its appearance under the microscope as large, rocky particles, it seems likely to be the natural mineral form.
The cheaper blue pigments, indigo and smalt, are conspicuous by their absence.
Greens Malachite (basic copper carbonate, CuCO3.Cu(OH)2) was identified as the brilliant, rather bluish green in landscape and foliage. Under the microscope at about 125 x it is seen as angular, rocky particles, similar to those of azurite, above (as distinct from the 'globular' particles of a green copper carbonate pigment described in this ‘Bulletin’, p.23 and p.65 in connection with pictures by Giovanni di Paolo and Giovanni Bellini). It can be seen in a paint cross-section from bright green foliage in Plate 6e (p.47). The pigment is by no means as frequently-occurring in easel painting as its blue counterpart, azurite, but similar examples of what, as here, seem to be the mineral form, have been identified by us in pictures by Tintoretto and Veronese.
Verdigris (basic copper acetate, Cu(C2H3O2)2.2Cu (OH)2) and copper resinate green seem to comprise the remainder of the landscape and foliage greens and include some green glazes which have become brown with age. Verdigris can be used as a powder pigment mixed with a medium in the usual way, but seems often to form the starting material for transparent green glazes made by dissolving it in a resinous or oleo-resinous medium of some kind. Its regrettable tendency to discolour to shades of brown or even black with age and exposure is discussed elsewhere in this ‘Bulletin’ (p.49). It would have been in demand about the time that the more naturalistic treatment of landscape was developing under the influence of Giorgione and Titian, in order to extend the range of green shades available, for it can be used as a final modifying glaze or in mixtures with other pigments in various combinations. In the ‘Bacchus and Ariadne’ some final greens have browned; a browned copper resinate glaze in which under the microscope a few green verdigris particles are still perceptible is seen in Plate 6f, p.47). Here the foliage had been applied as a single glaze layer over the blue paint of the sky, making it very vulnerable to effects of light. It is known, incidentally, that the change of colour from green to brown in this sample from the leaves around the raised arm of the satyr at the extreme right must have taken place, for in an early seventeenth century copy of the ‘Bacchus and Ariadne’, sometimes attributed to Poussin, and lent from the Duke of Northumberland's collection for the exhibition in 1969 of the newly-cleaned original, the same leaves are depicted as green. Compared with some early works of Titian, the green colours in the ‘Bacchus and Ariadne’ are miraculously well-preserved. The appearance of the ‘Noli Me Tangere’ (No.270) must originally have been very different, for the brown foliage of the large tree and much of the landscape has been identified as discoloured copper resinate green. By contrast, it was interesting to discover that the orange-brown tree which figures in the top right corner of the ‘Bacchus and Ariadne’ is painted in ochre (iron oxide) colours, with no trace of browned copper resinate. Its appearance would suggest an autumn landscape, but for the fact that other plant life depicted, such as the iris and columbine and the tender young vine shoots, seem to typify late spring or early summer. Titian may have introduced the brown tree to provide a patch of warm contrasting colour in that area of the picture. Green earth (a complex silicate mineral, containing iron and magnesium; usually celadonite). This grey-green pigment can be seen as the lowest layer of underpaint for a brighter green of foliage in Plate 6e (p.47). It was also identified as a minor component of flesh paint in the greenish shadow of Bacchus's left forearm.