NOTES ON PRELIMINARY DIAGNOSTIC TESTS

Ultraviolet (U.V.) fluorescence tests

Fluorescence from ultraviolet rays highlights the plastic aspect of the figure of the Saint and of the architecture, particularly the area of light on the right of the painting, where the shadow "cast" by the figure of the Saint remains quite visible. The U.V. diagnostic images highlight the areas that were retouched after drying and reveal the presence of an organic binder. In particular, the strong fluorescence from the parts refinished in tempera grassa (that is, lead-based white with protein agglutinates plus oil) like, for example, the points of light on the staff, the white dress of the figures decorating the strip bordering the azure mantle, a few finishing touches on the book, the white points on the miter and, again on the miter, several oval and rectangular geometric figures in imitation of precious stones. Much less evident, because of their low level of U.V. fluorescence, are the areas with azurite, such as the mantle and the clothes of the figures decorating the strip that borders the azure clothing of the Saint. The face also presents a level of fluorescence, confirmed by chemical analyses, indicating the presence of tempera, which the restoration may determine to be original or repainted.

It is also interesting to note that the fluorescence of the gloves has been shown to be very similar to that of the highlighting in CaCO3 (calcium carbonate, or San Giovanni white) of the transparent clothing of the Annunciation Angel in the cycle of the Legend of the True Cross in the church of San Francesco in Arezzo.

Infrared Reflectographic Tests (I.R.)

Infrared reflection tests have played an important role in preliminary scientific studies. Exploiting the principle that different painting materials show different levels of transparency on exposure to I.R. radiation, reflectographic tests permit an elevated optical penetration which, exploiting greater wave lengths than those utilizable by I.R. photographs, allows the visualization of pictorial elements otherwise hidden by the thickness of the material, and not directly traceable by other investigative methods. Relectography also offers the great advantage of allowing real time observation by use of a closed circuit video system. In fact, the images transmitted to the monitor (by a video camera equipped with a cathode tube, sensitive to visible radiation and to infrared radiation less than 2200 nm) can be analyzed directly and selected for subsequent electronic elaboration - video recording on tape, digitalization, recording on magnetic or optic disks, etc.

The application of I.R. reflectography in the specific case of Piero della Francesca's Saint Ludovico furnished useful information for an improved understanding of painting techniques, such as dusting ( as in the illustrations shown here which compare the visible images to those taken from I.R. reflectographic tests). I.R. reflectographic tests also made it possible to read and analyze details obscured by accumulated dirt, layers of decaying fixatives, or saline efflorescence, facilitating the identification of abrasions of the painted surface and repainted areas.