A preliminary study was conducted in the laboratories of the Opificio delle Pietre Dure in Florence to determine the condition and composition of the patina on the Fonte Gaia marbles. The results were fundamental to evaluating the course of action to clean della Quercia's marbles and determine the tools that would be necessary. The study, published in 1990, consisted of the analysis of more than 30 samples taken from various parts of the monument, for example Eve's right forearm or Adam's foot. Each specimen was tested using several methods, such as: X-ray diffractometry, infrared spectroscopy, optical microscopy with reflected light, and specific spot tests to reveal the presence of any organic material. The tests identified the principal components of the patina and encrustations as gypsum, calcium oxalate, silicates, and carbon particles. The patina was composed primarily of hydrated oxalates of calcium: weddellite (CaC2O4 2H2O; not inferior to 80 per cent and often around 95 per cent); and whewellite (CaC2O4 H2O). The film varied in colour from a light honey to a darker orange, depending on the marble's surface.

In the case of the Fonte Gaia marbles it is probable that the patina was the result of the deposit of organic material which over time was transformed via a gradual process of mineralization to oxalates. Such findings are not unusual, especially for marble sculpture that has spent extended periods outdoors. The external patina on such monuments is generally characterized by a yellowish hue caused by the presence of calcium oxalate. This film may then be partially covered by other darker hues, even black, made up of deposits of gypsum and carbon particles. The thickness of the patina may vary from 30 to 100 μm on the same monument. Occasionally small, round black holes appear on the patina. This type of damage is known as pitting and can create small black cavities in the underlying stone evident under a microscope and, at times, even to the naked eye, as attested on the Fonte Gaia. Generally, the patina is not soluble by rain, even acid rain, and hence is sometimes considered beneficial since it protects the marble from acid attack from the atmosphere.