The Structural Conservation of Panel Paintings

in the earlywood. In spruce, along a given earlywood tracheid, the large

bordered pit pairs on the radial walls occur singly and only occasionally

are paired; in larch, tracheids with many consecutive paired pits will be

commonly found (Fig. 10a, b).

If no resin canals are seen on the transverse surface with the hand

lens or if a tangential section reveals no fusiform rays, the wood may be

fir. Microscopic examination of a radial section will reveal that ray tra-

cheids are absent and that all rows ofray cells are of the same type of

cells—ray parenchyma. The cross fields have multiple small pits called

taxodioid pits, rounded pits with narrow borders appearing like the capital

letter O (Fig. 9c).

It is always possible that the unknown wood under consideration

is none of those described here. If the features of an unknown do not seem

to agree closely with any of the woods described here, it is necessary to

consult the literature to pursue a more thorough investigation. For example,

there are numerous other pines that also have large resin canals but non-

dentate ray tracheids or other types of cross-field pitting. For example,

other softwoods that have been found in painting panels include the true

cedars, Cedrusspp. (cedars may also contain resin canals and fusiform

rays), and Mediterranean cypress, Cupressus sempervirens(containing longi-

tudinal parenchyma, vertically oriented cells occurring among the longitu-

dinal tracheids; they have dark contents, conspicuous when observed

microscopically).

Hardwoods

The hardwoods can be roughly classified by examination of transverse

surfaces with a hand lens and evaluation of the size and arrangement of

pores. If the wood has relatively large pores grouped into the first-formed

portion ofthe growth ring, forming a conspicuous zone, the wood is

I  W  P P 29

a bc

Figure 9a–c
Radial sections of (a) Scots pine (Pinus
sylvestris)showing a portion of a ray: the
upper two rows ofray cells are dentate ray
tracheids, and the lower four rows of cells are
ray parenchyma with large windowlike cross-
field pitting; (b) spruce (Piceasp.) showing a
portion ofa ray; the upper and lower two
rows of ray cells are ray tracheids, and the
central two rows of cells are ray parenchyma
with piceoid cross-field pitting; and (c) fir
(Abiessp.) showing a portion ofa ray: all ray
cells are ray parenchyma with taxodioid cross-
field pitting, and crystals are present in the
third row (counted from the top) ofray
parenchyma.

ab

Figure 10a, b
Radial sections showing bordered pits on
radial walls of longitudinal tracheids in early-
wood. In (a) spruce (Piceaspp.), bordered pits
are usually unpaired; and in (b) larch (Larix
spp.), bordered pits are commonly paired.