Samenvatting Manual of housekeeping
H22
Metals deteriorate because, unlike most other materials, they are readily affected by chemicals in
the environment (7 Chemicals).
Where this layer is considered aesthetically pleasing it is called ‘patination’, where unaesthetic,
‘tarnishing’.
The speed at which corrosion occurs varies considerably: some metals are more reactive than others
and are likely to corrode whatever the circumstances. In fact, metals can be placed in a scale of
reactivity from highly reactive base metals, such as zinc, through iron, tin, lead and copper to the
much less reactive silver and gold. However, the corrosion rate of most metals is much faster if
water is present, whether as damp, condensation, high RH or deposits on the surface held by
absorbent materials such as dust.
bimetallic corrosion
Corrosion is even more rapid if chemicals are present
Copper and its alloys are much more stable, but over time
they too slowly develop a tarnish of dark brown/red oxides
and sulphides. Tarnishing can appear ‘streaky’ where
lacquer has been unevenly brushed on or rubbed off.
Copper and its alloys are particularly susceptible to certain
salts, such as chlorides in sweat or sea air, or acetates from
oak or vinegar. These soon form spots or crusts of green
corrosion products, irreversibly etching the metal below.
Most dust-free metalwork is relatively stable at 50–65 per
cent RH.
The other major type of deterioration is physical
Wear and scratching of a metal surface is common from
repeated handling and cleaning.
Light
Being organic, lacquers deteriorate particularly in light, resulting in a darkening effect and/or an
acceleration of the corrosion of the metal beneath. However, like corrosion, the darkening of
lacquer can sometimes contribute to the creation of patina on a metal surface.
Cast iron
Cast iron has a number of types of deterioration particular
to itself. Because it is brittle it can break if dropped. The
rapid change in temperature caused when a fire is lit in a
grate can cause the cast iron to fracture, and long periods
of heating may cause serious distortion. Repeated heating
over a long period also ‘burns’ the cast iron: the iron
becomes oxidized, leaving a brittle porous surface which
can suddenly flake off.
Past repairs
In some cases a repair may have unnecessarily damaged
H22
Metals deteriorate because, unlike most other materials, they are readily affected by chemicals in
the environment (7 Chemicals).
Where this layer is considered aesthetically pleasing it is called ‘patination’, where unaesthetic,
‘tarnishing’.
The speed at which corrosion occurs varies considerably: some metals are more reactive than others
and are likely to corrode whatever the circumstances. In fact, metals can be placed in a scale of
reactivity from highly reactive base metals, such as zinc, through iron, tin, lead and copper to the
much less reactive silver and gold. However, the corrosion rate of most metals is much faster if
water is present, whether as damp, condensation, high RH or deposits on the surface held by
absorbent materials such as dust.
bimetallic corrosion
Corrosion is even more rapid if chemicals are present
Copper and its alloys are much more stable, but over time
they too slowly develop a tarnish of dark brown/red oxides
and sulphides. Tarnishing can appear ‘streaky’ where
lacquer has been unevenly brushed on or rubbed off.
Copper and its alloys are particularly susceptible to certain
salts, such as chlorides in sweat or sea air, or acetates from
oak or vinegar. These soon form spots or crusts of green
corrosion products, irreversibly etching the metal below.
Most dust-free metalwork is relatively stable at 50–65 per
cent RH.
The other major type of deterioration is physical
Wear and scratching of a metal surface is common from
repeated handling and cleaning.
Light
Being organic, lacquers deteriorate particularly in light, resulting in a darkening effect and/or an
acceleration of the corrosion of the metal beneath. However, like corrosion, the darkening of
lacquer can sometimes contribute to the creation of patina on a metal surface.
Cast iron
Cast iron has a number of types of deterioration particular
to itself. Because it is brittle it can break if dropped. The
rapid change in temperature caused when a fire is lit in a
grate can cause the cast iron to fracture, and long periods
of heating may cause serious distortion. Repeated heating
over a long period also ‘burns’ the cast iron: the iron
becomes oxidized, leaving a brittle porous surface which
can suddenly flake off.
Past repairs
In some cases a repair may have unnecessarily damaged
