Madonna Suckling the Child
The image follows the traditional practice of Italian Renaissance painting. The wooden panel, in this case made of poplar wood, would have been prepared by the application of a smooth gesso ground to the painting side. Gesso is slaked Plaster of Paris, (calcium sulphate), and would be bound together with animal glue, applied as a paste and worked to a smooth surface once hardened. Two layers were often applied, the first being a coarse mixture (gesso grosso), the second being a finer layer (gesso sotile).
After preparation the next stage would be to apply an underdrawing or preparatory layout of the design. This might be applied directly to the surface, either drawn in charcoal or silverpoint or painted in a carbon black based paint applied with a fine brush. Alternatively, for designs taken from other images or those reproduced within a particular artists’ workshop, the drawing might be transferred from a ‘cartoon’ or study drawing by a variety of means.
Tracing could be used, or the design might be reproduced by dusting charcoal powder through holes pricked around the outlines of the drawing onto the panel below. This process is called ‘pouncing’. Subsequent layers of decoration, from areas of gold leaf to the oil paint layers themselves, would be applied over this drawing preparation. In many paintings some of the underdrawing remains visible to the naked eye, but in others it remains hidden under the paint layers.
For many paintings from both Northern Europe and Italy in the 15th and 16th centuries, identifying the underdrawing can play a crucial part in understanding the image, either by establishing its design origins or in some cases confirming authorship to a particular school or individual artist. The importance of infra-red investigation is that it can often show up this underdrawing quite clearly, whereas neither ultra-violet nor x-ray techniques can pick up this information.
Investigating the painting
The varnish on the painting is quite thick with a dull, waxy surface and there seem to be disturbed areas of paint underneath it. The image is difficult to see properly so it is difficult to determine the condition of the work. Even though we know that this painting was last worked on in 1971, there are insufficient records of what was done to tell us enough about the condition of the painting before considering any treatment.
Before any conservation work can be done to a painting we need to know as much as possible about its current condition, including the nature and location of any paint defects or structural problems. There are a number of different ways in which information about the current state of a work can be determined.
Examination under ultra-violet radiation
Ultra-violet (UV) light is used as a surface identification technique. It relies on the fact that UV light, which is invisible to the human eye, can induce visible fluorescence in some materials. This can show up a number of features, including the presence of natural resin varnishes, as these often fluoresce with a milky green colour under UV light.
The painting viewed under UV radiation
Retouchings on top of a varnish can also be identified, as oil paint does not fluoresce under UV, so retouchings appear as dark patches on the varnish surface. Anything else on the surface masking the fluorescence of the varnish will also appear dark. Certain pigments also fluoresce with different colours under UV, so this may help to show where they have been used. Most UV examination lights emit around the 350-360nm region (UVA) but are usually filtered to absorb any visible and short wave UV radiation.
The colour UV image shows a number of significant features. There is an overall pale milky green fluorescing layer, probably indicating the presence of a resin varnish such as mastic or dammar. There are darker areas masking the fluorescence over this, which represent retouchings applied by the last restorer who worked on the painting in 1971. In addition to these patches of applied paint there are some paler additions visible, particularly on the Child’s body and the Virgin’s face. These probably represent older retouchings which appear to be under the natural resin varnish.
We know from the x-ray (see below) that there are large losses to the original paint in the area adjacent to the Child’s head, so it is interesting that retouchings and repaint in these areas do not appear to show under UV, because they are hidden by the varnish. These restorations may be much earlier. The painting may also have a modern synthetic varnish coating, which does not fluoresce in the same way and is therefore not visible under UV.
Examination under infra-red radiation
Infra-red (IR) radiation can penetrate very slightly below some varnish and paint layers and is most often used to identify underdrawing on an image that may not be visible to the naked eye. The success of the technique depends on materials or layers that absorb the IR wavelengths lying below layers that are transparent to IR. Carbon used for underdrawing usually absorbs IR and appears dark, while paint and varnish are usually transparent under IR. Therefore carbon line drawing beneath paint or varnish may show up.
The painting viewed under IR radiation
The IR source is usually a tungsten bulb and the resultant reflected image can not be seen by the naked eye. It must be recorded with a special vidicon camera with an IR sensitive tube and viewed on a screen, or by a digital camera with an IR sensitive CCD (charge coupled device). Near IR radiation of wavelength between about 1000-1500nm is most commonly used for identifying underdrawing features on paintings.
The IR image gives a different view of the painting and a new layer of information. The darker areas are absorbing IR radiation and may contain copper based pigments such as some greens and blues which absorb IR quite strongly. Lighter areas of paint often reflect more IR.
Of specific interest is the drawn outline that is visible around the body of the Child, particularly distinct on the legs and arms. This is the underdrawing, or outline preparation of the design, which may have been taken from a pattern or cartoon, or drawn freehand. There are few other distinct lines visible, apart from the edges of the Virgin’s proper right hand. This is quite a simple example of underdrawing, though other examples can reveal very complex preparatory outlines.
Examination under X-ray radiation
As with medical radiography, this technique employs radiation that can entirely penetrate the materials of a painting. This can often show internal structural features, as well as features of the paint layers themselves.
The painting viewed under X-ray radiation
The success of examination using X-ray radiation is dependent on there being materials of differing densities present in the structure, without any one layer being of too high a density. If one layer is very dense, (a thick priming layer with lead white paint, for instance), an x-ray of the painting may give little useful information, as the lower density differences will be masked by the high density layer.
The x-ray image shows all the different densities of the materials in the painting. The most striking features are the iron nails around the sides of the panel, which show up as very dense (white) on the image. These have been used to attach wooden strips at the side of the panel and iron strips along the top and bottom edges.
The iron strips were intended to prevent the panel from warping but are probably causing stress to the wood. The side strips were applied to help fit the painting into its frame. Over the rest of the image most of the painted design can be seen but there are darker areas (lower left corner and right of the Child’s head) where the original paint has been lost.
Some of the smaller dark losses follow the wood grain of the panel. This is a common feature of panel paintings, where movement of the wood causes paint losses along the grain. These losses have been filled and retouched in the past, so the x-ray is the only way of identifying where they are.
Another noticeable feature is the thick pale white line running up the centre of the image. It is not certain what this is. It doesn't appear to be damage or a later addition but could be a filling applied to a flaw in the panel before even the gesso or paint layers were applied. Over much of the surface the network of very fine age cracks in the paint show up as thin dark lines in the paint, again mainly following the wood grain of the panel.