Conservation of Ancient Timbers from the Sea 297
to the principle of minimum intervention, and the best conservation method
is one that interferes with or modifies the wood to the least extent.
4.1 Definitions and Aims
The types of chemical treatments involved in the conservation of archaeo-
logical wood are: (i) lumen-filling treatments that fill the spaces within the
wood with an inert chemical to provide structural support and prevent col-
lapse, (ii) bulking treatments that enter the cell walls and reduce cell wall
shrinkage, and (iii) surface coatings that cover the surface of a dry object.
4.2 Lumen-filling Treatments
Large amounts of a high molecular weight chemical are introduced into the cell
lumina and permanent voids (Figure 12) to improve the physical properties of
the object and to prevent cellular collapse of very decayed wood cells. This
treatment must form a solid in the cell lumina and voids as water is removed.
However, there is one major drawback to lumen-filling treatments in that
they can cause osmotic collapse if too great a concentration is employed across
the wood cellular structure. Since the mass transfer of a chemical into wood
is proportional to this concentration gradient, the result is an extremely slow
process. Calculating a maximum sustainable concentration gradient, and length
of time taken for an object to equilibrate at each concentration step, is one of
the most fundamental issues that conservators face when devising a lumen-
filling treatment method. Previously, this often involved a certain amount of
Figure 16An SEM of oak fibre showing decay of the secondary wall layers (hemicellulose
and cellulose component). Note the residual lignin component in the cell