The Structural Conservation of Panel Paintings

Microscopic examination

For microscopic examination of wood, thin sections taken from the trans-

verse surface are sometimes useful, but the most valuable information is

usually found in radial and tangential sections. Examination of a cleanly

cut end-grain surface with a hand lens reveals the orientation of radial and

tangential directions in the area of the wood sample under scrutiny, and

accessible surfaces can be split or shaved down along the radial and tan-

gential planes in the grain direction. The tangential plane is formed paral-

lel to the growth rings, the radial plane perpendicular to the growth rings.

Figure 2 illustrates the principal planes of wood structure and the prepara-

tion of small areas ofradial and tangential surfaces with respect to the

transverse surface.

During work on painting panels, it is often possible to cut sections

directly from a corner edge of the panel. In other cases it may be more

expedient to use material removed in conservation work or simply to

remove asmall piece for identification. A piece 3 333 10 mm will typi-

cally be sufficient.

From the surface ofany of the principal planes of the panel or

wood sample, a tiny slice of tissue is carefully sliced offwith a razor blade.

24 Hoadley

a bc

Figure 1a–c
Woods can be initially classified into general
types by examination oftransverse surfaces
with a 10 3 hand lens. Examples shown are
(a) a softwood, pine (Pinus sylvestris), (b) a ring-
porous hardwood, ash (Fraxinussp.), and (c) a
diffuse-porous hardwood, maple (Acersp.).

a

b

Figure 2a, b
Block of softwood (Pseudotsuga menziesii,
Douglas-fir) (a) machined to expose principal
planes: X 5 transverse(cross-sectional or end-
grain); R 5 radial; T 5 tangential. A small
portion of the end-grain edge of this panel of
poplar (Populussp.) was surfaced with a razor
blade (b). On this exposed transverse surface,
the anatomical orientation is revealed on the
basis of the growth ring and ray placement.
The upper right corner was beveled parallel to
the rays to produce a radial plane. The upper
left corner was then beveled parallel to the
growth ring to produce a tangential plane.
From the surfaces of any of these principal
planes, thin tissue sections can be taken for
microscopic examination.