Series editors' preface - Wood Tools

668 Conservation of Furniture
Ivory may be cleaned using the dry cleaning
methods described in section 11.2.4. A
traditional method using dilute hydrochloric
acid to clean ivory is known to strip the
mineral component from the ivory, eroding the
surface, opening cracks and causing increased
hygroscopicity. Matienzo and Snow (1986)
demonstrated that immersion in toluene can
cause an increase in the concentration of
organic material on the surface but observed
that ethanol and acetone caused no noticeable
change. Aromatic hydrocarbon solvents should
be avoided, though as yet the effects of
aliphatic hydrocarbons have not been quantified.
Given the hygroscopic nature of ivory and
bone, non-aqueous methods for the removal of
surface dirt, such as a swab slightly dampened
with white spirit, ethanol or acetone may be
preferable. In some cases, however, the most
efficacious method for removing dirt is a swab
slightly dampened with saliva or deionized
water. Care should be taken to avoid dimensional
distortion by minimizing contact with
water. Some sources recommend a contact
time of fifteen or twenty seconds followed by
immediately drying the surface (CCI Notes
6/1). Solvent mixtures which combine white
spirit, acetone and water may also be effective.
Whilst a soft brush may remove dust and dirt
from the surface, embedded dust, wax and
accretions of dirt may be more difficult to
remove, particularly when the surface of the
ivory is damaged or cracked. Poulticing (see
section 11.6) may be effective in such cases.
Cracks in ivory veneer may be partial or run
through the whole thickness of veneer. In
cases where ivory veneer is already loose,
lifting the veneer completely may give better
access for cleaning. Patience may be required
to avoid causing further damage. Water is
often used to soften residual adhesive, though
isopropyl alcohol may be used if there is no
risk of damaging adjacent materials or surface.
Partial cracks may be cleaned using a mediumsoft
brush and solvent. Poultices may be used
to remove deep accretions of wax.
Staining
Whilst yellowed ivory that has been kept in
the dark may be whitened by simple exposure
to light, removal of other stains, such as rust
or copper stains, ink or previous use of
adhesives such as animal glue or shellac may
be more problematic. Darkened residues of
animal glue may have penetrated into the
body of ivory and the problem is usually
exacerbated with porous bone. Oils, both
drying (e.g. linseed) and non-drying (e.g.
almond) may have been applied in the past
to saturate the surface and produce a low
sheen. Oiling ivory is no longer considered an
acceptable conservation practice. Whilst
almond oil can usually be removed with white
spirit, linseed oil that has darkened and
crosslinked may be more problematic.
The first step in the treatment of such stains
is to decide whether stain removal is desirable.
Many stains are considered of value because
they contribute to patina, an appearance of
age or evidence of history of use. Stain
removal is often very difficult. Excesses of the
past have led to a general presumption against
bleaching because of the difficulty of keeping
such treatments localized, their irreversibility
and the inherently chemically destructive
nature of the process. Occasionally localized
bleaching may be undertaken, though care
must be taken to avoid the formation of a
bleached halo around a stained area. Inlay to
be bleached is usually removed from the
substrate to increase the effectiveness of the
treatment (stain are often taken up from the
verso side) and to avoid damaging adjacent
material. Bleach should be carefully applied to
the affected area only. Hydrogen peroxide
may be used though it is not combined, in this
instance, with a base such as ammonia or
sodium hydroxide (see Bleaches under section
13.5.3). Progress should be checked regularly
and the action of the bleach may be noticed
within fifteen to thirty minutes or longer.
Sodium hypochlorite bleaches should not be
used as they have been associated with
yellowing of ivory weeks or months after the
treatment and because they degrade to sodium
chloride, giving rise to the potential for salt
damage.
Some success has been reported in removing
metal stains with chelating agents (Rao and
Subbaiah, 1983). There is a possibility that
chelating agents may attack mineral components
of the ivory. Conditional stability
constants should be considered in relation to
pH and the sensitivity of the ivory or bone to
excessively acidic or alkaline conditions (see
section 11.5.5).