Series editors' preface - Wood Tools

450 Conservation of Furniture
(a)
(b)
Figure 10.9 Abrasives
(a) A plate from J.A. Roubo, Le Menuisier ebeniste
(1772) illustrating eighteenth century abrasives, including
scrapers, sharkskin, polishing sticks and Dutch rushes
(obtained from members of the Equisitaceae, the
horsetail family of jointed ferns, whose stems contain
large amounts of silica). (b) Some traditional abrasives,
including a bundle of Dutch rushes, emery, rottenstone,
glass and pumice
variety of materials are used for the particles on
abrasive papers and these vary in their hardness
(see Table 10.3). Harder particle papers may be
more appropriate for harder woods.
Abrasive papers vary in the nature of the
material used to bond the particles (e.g. some
are waterproof), how much abrasive is adhered
to the paper, and the thickness or weight of
the backing paper. Mesh sizes for abrasive
particles refer to the number of openings per
square inch in the wire screens used to grade
them. Mesh sizes range from coarse (80) to fine
(1000 or more). Those up to around 180 grit
are used to level bare wood. After around 180
grit the scratches produced by the abrasive are
smaller than already exist on the surface of the
wood and thus they do not affect the overall
appearance of roughness. Given that the lower
the number the coarser the grit, an 80 grit
paper will remove stock rapidly and is suitable
for coarse work, whilst a final surface may be
produced with 180 grit paper.
Abrasives work by a cutting or grinding
action that scratches and removes a small
amount of surface. Abrasives vary in hardness,
particle size and the manner in which they are
applied (powder, paste or adhered to a backing
such as paper). Harder abrasive particles
will remove more of the surface with each
comparable motion, but particle size will determine
whether the scratches produced will be
visible. The abrasive effect of particles on a
surface is ameliorated by the presence of a
lubricant, such as solvent or wax. The conservator
may need to take measures to control
exposure to abrasive powders, the dust
produced or solvents used as lubricants.
The Mohs Hardness Scale is a comparative
scale using various minerals as standards:
talc 1
gypsum 2
calcite 3
fluorite 4
apatite 5
orthoclase 6
quartz 7
topaz 8
corundum 9
diamond 10
Materials of Mohs hardness 1–2 can be
scratched by a finger nail, those of Mohs hard-