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around the crack in the calf revealed very
poor quality material in the original
casting and a large number of dowels that
would significantly weaken this area.
However, the thickness of the skin casting
was relatively consistent over the whole of
the statue.
To carry out a repair in this area that
would be structurally sound rather than
just cosmetic, it would therefore be
necessary to remove the band of material
that incorporated all of the disturbed
material around the crack, and as many of
the dowels as possible, while still being
consistent with the constraints imposed
by English Heritage. This was achieved
by removing all of the cracked and
damaged material and then cutting back
the edges of the hole until sound material
was reached. Two cast aluminium inserts
were then prepared using moulds from
the Victoria and Albert Museum. The
inserts were to be welded in using a
tungsten inert gas technique. To
overcome shrinkage problems across the
joint, that might possibly cause either
distortion or cracking in the statue, the
welds were as narrow as possible and built
up using fine rods.
The thigh was found to have a plate
varying in thickness between 1.5 and 4
mm; the bursting had been caused by a
build-up of corrosion products behind
this plate. Replacing such a thin patch
would have been impractical the same
problem would probably recur in the
future. It was therefore recommended
that the plate be completely removed and
the area repaired by building up with
weld material before dressing back to the
original contour.
It was also recommended that the
statue be supported by securing the
armature, rather than bolting of the
flange around the foot as was done
previously. This will relieve some of the
stress in the disturbed calf in future.
Although consumables were chosen to
match the original casting, problems were
encountered with cracking during
welding. It was not
possible to provide
a normal pre-heat,
and following the
first attempt at
welding, cracking
was observed along
one side of the
weld. After this
had been removed,
the statue was
carefully lagged
and hot air
blowers used to
apply a gentle heat
to the area to be
welded. This was
successful in
overcoming the contraction cracking
although examination after completing
the weld run revealed a different type of
cracking in the centre of the weld. This is
known as liquation, or solidification,
cracking of the final metal to solidify. Also
seen were small blisters or bursts in the
original cast material adjacent to the weld.
To assess the possible cause of these
problems, documentation of previous
examinations of the statue was reviewed
and the chemical composition for the
original casting was found to contain
small quantities of mainly silicon, copper
and iron.
The quantities of the alloying elements
present, when diluted with the pure
aluminium welding rod in the weld pool,
produce an alloy composition which is
most susceptible to solidification
cracking. This is due to the long freezing
range and the high shrinkage coefficient
for this material. To overcome this
problem, it was necessary to use welding
rods with an alloy content capable of
maintaining a lower solidifying range and
lower shrinkage characteristics even when
diluted into the weld pooi and for this
reason small diameter 12% silicon rods
were recommended.
The bursting in the original cast
material appeared to be due to surface
working of the statue resulting in
entrapment of material which, when
subjected to the heat of welding, rapidly
expanded causing this problem. It is
therefore necessary to reduce the heat
input to the weld and this is done by
using smaller diameter weld rods and a
lower melting point material, ie eutectic
composition 12% silicon weld rods.
The success of these recommendations
were proved by liquid penetrant
inspection of the welding and
surrounding casting after cutting back to
the final contours.
The repairs to the statue are not just
conservatorial but also of a structural
nature and represent an optimum
solution to achieve maximum strength
with minimum disruption to the statue.
Rumours abound each time the statue is
taken down, of it being replaced with a
replica. However, considering the time
that the statue has been on display, there
is little evidence of loss in definition due
to corrosion, even despite the urban
pollution, and if weathering should
continue at a similar rate then the statue
may remain outside for a great many
more years. Provided access to the statue
is restricted, to the extent that vandalism
can be prevented, then similar damage is
unlikely to occur in the future.

Simon Clarke is an Associate of the Metallurgy
Department at Sandberg Consulting. The article is
reproduced by kind permission of Materials World
Journal of the Institute of Materials.
Eros returns to site in Piccadily Circus ready for a good
many more years.
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CONTEXT 42

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