Series editors' preface - Wood Tools

Cleaning tests may embrace a wide range of
techniques such as mechanical cleaning, dry
cleaning, solvent and aqueous cleaning
(including the manipulation of pH, conductivity,
and/or the addition of chelating agents,
enzymes, detergents or surfactants). A cotton
swab or the corner of a lint-free cotton cloth
may be a convenient way to apply test material.
If cleaning solutions are used, the test
should start with the application of a small
amount for a very short time. The surface
being tested should be allowed to dry
completely before judging the full impact of
cleaning. If there is no unfavourable reaction,
longer times and larger amounts can be tried.
If a test clean proves satisfactory in one area,
several other small areas should also be tested
to ensure uniformity of the result before
committing to a course of action.
Ultraviolet light may highlight the degree of
change caused by the cleaning test. For
example, a brightly autofluorescing cleaned
test area may contrast with muted fluorescence
from the untreated coating. This suggests that
non-fluorescing dirt, oil and grime have been
removed and the naturally autofluorescent
coating below has been retained and revealed
through the cleaning process. Conversely, a
total lack of autofluorescence in the test area
may suggest that a coating has been removed
rather than enhanced.
The basic principle behind all cleaning is to
start with the least potentially damaging material
or technique. If ‘stronger’ solvents or
combinations are necessary, tests should
progress in measured increments. Solvents
may be combined with other cleaning
methods or techniques, for example using dry
cleaning materials in combination with hydrocarbon
solvents. The wetting and cleaning
properties of organic solvents may be
enhanced by the addition of a small amount
of a compatible detergent or surfactant.
11.1.6 Dirt
Dirt may be undesirable because it obscures
the aesthetic, informational or other properties
of an object, or accelerates the process of
deterioration. Dirt is generally hygroscopic,
often mildly acidic and may be characterized
by source, size, chemical composition, or the
mechanism by which it adheres to a surface.
Principles of cleaning 499
Air filtered from urban environments may
contain material such as industrial pollutants,
brick dust, salts, oils, waxes, clay, protein, lint,
pollen, mould spores and human skin. Surface
dirt on decorative objects has been characterized
as a combination of particulate material
and greasy or oily material (Phenix and
Burnstock, 1992). The particulate material
varies in chemical composition, surface characteristics,
size, shape and hardness and may
include inorganic material and elemental
carbon. Particles may be present in a range of
sizes but are generally so finely divided that
they exhibit colloidal properties. Carbon black
and other solid particles can attract and absorb
acid and alkaline agents, and oxidizing and
reducing agents, from the surrounding atmosphere.
This absorption can result in the formation
of acid solutions where moisture is
present and promote hydrolytic, oxidative or
reductive breakdown of sensitive materials.
Dirt that contains metal ions has a catalytic
effect on the deterioration of some materials.
Greasy or oily material composed of hydrocarbons
and fats may contain free acids and
also assist the adhesion of particulate matter
to the surface. Dirt is discussed further in
Chapter 6.
Surface grime may be a result of historical
use and such dirt may have value in assisting
in the interpretation of the object. Dirt can be
separated into that which has been deposited
on the object and that which is a result of the
object’s own degradation processes. To
remove the latter is to take away some aspect
of the object’s original material and it is therefore
essential to consider the nature of the
object and how its surface relates to its history
before any cleaning is undertaken.
The probability that dirt will be removed by
a cleaning treatment depends on the type and
strength of the adhesion between dirt and the
surface of the object. Dirt may adhere to a
surface coating mechanically by physical
entrapment, as a result of static electricity, by
hydrogen or dipole bonding or by van der
Waals forces (Moncrieff and Weaver, 1992). It
is usually a combination of these forces that
results in dirt accumulating and remaining on
a surface. The particle size of the dirt also
affects how it is fixed to the surface. Larger
particles of dirt (>1 μm) are held to a surface
largely with electrostatic forces and can be