Series editors' preface - Wood Tools

General purpose protease gel
100 ml deionized water
0.73 g TRIZMA Pre-Set buffer (Sigma
T-4253, pH 7.6)
0.1 g Brij 35 (polyoxyethylene 23
lauryl ether)
2 g methyl cellulose (4000 cps)
10 mg trypsin (Sigma Type I, T-8003,
1 mg =10 000 BAEE units)
At the end of a treatment, enzymes should be
denatured to prevent any further reactions.
Enzymes are water-soluble and an aqueous
rinse is therefore appropriate. Raising or
lowering pH, temperature, the use of denaturing
solvents, exposure to air or the application
of inhibitors may be used as a means of
preventing further enzyme activity. Given that
lipase must be refrigerated and contact with
oxygen minimized to ensure the enzyme is
not denatured before it is used, simply air
drying Lipase Type VII at room temperature
will denature any enzyme residue (Wolbers,
2000).
In their dry form, enzymes should be stored
carefully according to the manufacturer’s
guidelines. Dry enzyme preparations have a
shelf life of about one year when refrigerated.
As biologically derived catalysts, enzymes will
catalyse reactions on and in the human body.
Conservators may be exposed to airborne
micro-fine powder or splashes when measuring
and mixing enzymatic cleaning solutions
if simple safety precautions are ignored.
Precautions that should be taken when
working with enzymes include avoiding inhaling
enzyme powder, avoiding contact
between powder and eyes, skin and mucous
membranes; wearing suitable protective clothing,
e.g. masks, goggles, and gloves; working
in a well-ventilated, but not draughty,
environment; and avoiding contact between
liquid enzyme preparations and skin and
mucous membranes. Most people will not
experience any obvious adverse effects, but
some individuals may experience an allergic
response. Conservators who suffer from
asthma or other respiratory complaints,
eczema, dermatitis and hayfever may wish to
avoid using enzymes. Spills should be wiped
up with a damp cloth, as all enzymes are
water-soluble and the priority should be to
avoid inhaling enzyme dust.
Principles of cleaning 551
11.5.7 Blanching and blooming
The literal meaning of blanching is to make
white by withdrawing colour, and is used to
describe an opaque whitish appearance that
occurs because of a defect in the paint film
(Groen, 1988). Blooming is also an opaque
whitish effect but occurs in varnishes, often as
a result of exposure to moisture or water. The
term blooming has also been used to describe
optical changes caused by efflorescence. These
terms are often imprecise and often used interchangeably.
They do not identify the cause of
the problem but indicate that the optical
properties of a surface have been altered.
Efflorescence describes a whitish layer
encountered on the surface of a material, the
components of which originated in the material
itself. It may occur independently or as a
result of a cleaning treatment. It may occur on
wax layers. Efflorescence on oil bound painted
surfaces has been ascribed to the migration of
free fatty acids, such as palmitic and stearic
acids, from the binding medium to the surface
of the paint layer (Ordonez and Twilley,
1998).
Blanching may occur as a result of cleaning
with organic solvents, reagents, aqueous
solutions or consolidation treatments. It may be
a result of mechanical disruption of the surface,
such as abrasion during cleaning. Granular
redeposition of varnish can occur if a fastdrying
solvent is used for varnish removal. In
such cases the fault can be remedied by either
retreating with solvent or revarnishing.
Molecular clusters of water or solvent may
be included in a varnish or paint film after
cleaning or consolidation. This is common, for
example, after treating blisters with a waterbased
adhesive (particularly in combination
with heat), if aqueous solutions have been in
contact with water-sensitive areas of the
substrate, or as a result of excessive contact
time. It may be possible to optically resaturate
the affected area by applying fresh varnish. In
some cases it may be possible to remedy
blanching using a heated spatula isolated from
the surface with Melinex/Mylar.
Natural resins are weakly acidic materials
that become more acidic as they age and
oxidize. Some very degraded natural resin
surfaces may be partially soluble in water with
a pH of only 8–8.5, a fact that has been