Examples of stratigraphic investigation of historic plaster revealing an earlier fresco decoration (a), and of a canvas painting revealing earlier versions of drapery (b)

Stratigraphic investigation is sometimes an essential part of the examination undertaken before conservation treatment. Small, defined test areas are selected on an architectural surface, sculpture or painting, and more recent layers are progressively removed to identify evidence of older decorative schemes.

Stratigraphic investigation helps

to deepen our understanding of the work. The findings can guide conservation decisions and inform further scientific examination, such as identifying a pigment and dating its use to help establish the age of a newly revealed layer.

Non-invasive imaging: comparison of visible-light photography (a) and infrared photography (b) to reveal the preparatory drawing

Non-invasive imaging: raking-light photography (c) to reveal lifting in the paint layer

A range of diagnostic investigations can be undertaken before conservation treatment, from non-invasive imaging to invasive chemical and biological analyses. These help identify the constituent materials and examine deterioration in detail, providing information about the artwork and informing treatment decisions.
Some non-invasive imaging techniques can be carried out directly by the conservator using visible-light photography (direct, raking and transmitted light), as well as ultraviolet or infrared illumination.
Certain qualitative chemical analyses can likewise be performed using diagnostic tests: identifying organic substances such as proteins, carbohydrates, starches, oils, waxes, saponifiable compounds and natural resins, or inorganic substances and pigments through tests for carbonates, sulphides, copper and metal alloys, iron and soluble salts.
Specialist expertise may be needed to verify these results or carry out more complex investigations.
Dorica Restauri works with diagnostic specialists experienced in cultural heritage conservation.

Examples of a historic fixed wooden strainer (a) and a new expandable stretcher (b)

A traditional canvas painting is attached and tensioned onto a wooden strainer or stretcher, generally made from softwood. Earlier supports had a fixed construction, with four or more wooden members, depending on the size of the painting, joined using various joints and sometimes adhesives or hand-forged nails. Over time, these fixed supports were largely superseded by expandable stretchers in which

(a) Woodworm treatment: placing infested objects in a sealed enclosure and vacuum-sealing it;
(b) introducing CO_² at a controlled temperature for long enough to cover the hatching of eggs

Wood-boring insects can seriously compromise the condition of wooden artworks, affecting both the wood itself and its surface finishes and polychromy.
Insects that lay eggs inside an object (such as a sculpture, frame, canvas stretcher or painted panel) include species in the family Anobiidae; Anobium punctatum, the common furniture beetle, is a typical example. Once the eggs hatch, larvae feed on the wood, growing and excavating characteristic tunnels before developing into pupae and then adults. The adult insects then emerge through the exit holes commonly visible on the object's surface.
A treatment often used by conservators on wood,