Series editors' preface - Wood Tools

adhere the unwanted varnish or dirt to the
surface and bringing these molecules into
solution in order to remove them from a
surface. An exception to this principle occurs
when water is used to dissolve inorganic salts,
in which case the primary ionic bonds of the
‘dirt’ are disrupted.
An ideal cleaning treatment would leave the
primary and secondary bonding of the
substrate intact. In order to do this the conservator
needs to understand the forces at work
in a solvent (e.g. degree of hydrogen/dipole/
non-polar bonding, aromaticity) and the likely
interactions between solvent and surface.
Successful cleaning requires that the intermolecular
forces within a solvent be matched
to the intermolecular forces within the
unwanted material (‘like dissolves like’).
Understanding the classification of solvents
and the different contribution of polar and
non-polar forces within them allows the
conservator to tailor their cleaning treatment
for a particular cleaning or layer removal
problem. Ideally, the conservator should have
a basic understanding of the chemistry of the
unwanted material, the underlying surface,
and the solvent/s that will be used to separate
the two.
11.3.1 Classes of solvents that may be
encountered in furniture conservation
Solvents are classified into broad groups that
share common chemical characteristics.
Although there are an enormous number of
solvents available, a few solvents selected from
different classes is sufficient for most cleaning
problems. Understanding solvent classification
will help the conservator to utilize the Teas
chart to formulate test procedures and tailor
their treatments. For example, if using solvents
to test the solubility of an unknown coating,
there is little point in selecting industrial methylated
spirits, ethanol and isopropanol. Although
they are different solvents, they are all in the
same class (alcohols) and thus have similar
intermolecular interactions. A sequence of
solvents for cleaning tests to assess the general
sensitivities and chemical character of the
unwanted material may include a solvent from
each class (e.g. aliphatic hydrocarbon, aromatic
hydrocarbon, alcohol, ketone, water). On the
basis of such tests, the conservator could then
Principles of cleaning 505
assess which solvents interact in a desirable way
to remove unwanted material without damaging
the substrate. If, using a sample solvent from
each class, it had been established that alcohols
were the most suitable for a cleaning treatment,
it would be possible to exploit the subtle variations
within this class to fine tune a cleaning
treatment. Within the homologous series of
alcohols, for example, the conservator could
select a fast acting and fast evaporating solvent
(ethanol), or a slower evaporating solvent
whose branched structure also slows penetration
(isopropanol, isobutanol).
A common solvent sequence in cleaning
tests is an aliphatic hydrocarbon, followed by
an aromatic hydrocarbon, an alcohol, a ketone
and lastly water. It is important to understand
that this does not represent a progression in
solvent ‘strength’. No solvent (or other cleaning
method) is inherently strong or weak, but
is more or less closely matched to the physical
and chemical properties of the unwanted
material and/or the substrate.
Hydrocarbon solvents
Molecules that contain only hydrogen and
carbon are called hydrocarbons. Differences in
size and configuration alter their physical and
chemical properties. Molecules that contain
only single covalent bonds between carbon
and hydrogen atoms are called alkanes and
have the suffix -ane. In the past alkanes were
called paraffins or iso-paraffins. ‘Normal’ (n-)
alkanes have a straight chain structure.
Hydrocarbons that contain a carbon atom
connected to three other carbon atoms, giving
a branched structure, are called isomers.
Isomers have same number and types of
atoms but in a different arrangement, which
can lead to different chemical and physical
properties. Hydrocarbons in which a carbon
atom is connected to four other carbon atoms
are given the prefix neo-.
Molecules that contain one or more double
covalent bonds are called alkenes and have
the suffix -ene. In the past alkenes were called
olefins. Alkenes are often present as impurities
in petroleum fractions. Molecules that
contain one or more triple covalent bonds are
called alkynes and have the suffix -yne. In the
past alkynes were called acetylenes. Alkynes
have no solvent usage. Five or six carbons
may form a stable ring or cyclic structure (a