At each event we ask for a volunteer to record their experiences and impressions.
These articles are published in our newsletter and eventually
appear here as an archive of our activities. Note that these are only
provided for reference, and are not endorsed by Event Leaders.
Interpretations can change often and rapidly in Geology, any
information stated should be verified from appropriate sources before
The Art Bronze Foundry •
Ardingly Sandstone and Tombstones at Fletching •
Teaching the Dynamic Earth •
NHM Earth Science Library •
The Vale of Wardour, The SW Wiltshire Anticline •
Harwich and Wrabness, Essex
Visit to The Art Bronze Foundry (London) Limited
16 February 2006
Round by the gas works in Michael Road near Fulham
Broadway is a restaurant ornately decorated with bronzes.
The Art Bronze Foundry is next door. One or two people
turned up and we waited, only to find that everybody else
was inside in the warm. The shop was just big enough for
Sculptures come in all sorts of material from papier
maché to ornately carved wood. This means that the first
stage has to be quite gentle. So the lost wax method is
First a negative is made. Macwax, a releasing agent is
sprayed on the model and then silicone rubber is applied
with a spatula. This method gives good, accurate coverage.
Three-dimensional models need a join. For example
the join on heads passes vertically through the ears. Locating
pegs help the two parts fit neatly together. Any errors
here will give a wonky bronze.
Silicone rubber is flexible, which helps separation, but its
flexibility is also a disadvantage. It has to be supported by
a plaster cast for the next stage to make an accurate representation.
The cast is made of casting plaster possibly
supported with scrim.
Now a positive is made. Molten wax is painted on to a
thickness of 1/16th 1/8th of an inch. This is an ideal thickness
for bronze casting. Thicker bronze would distort too
much as it shrinks on cooling and solid bronze could never
be used. More wax is swilled in to join the pieces. The
wax model is then separated from the silicone rubber
It is finely inspected and cleaned up to perfection. To help
inspection the wax is coloured red colour and lighting is
soft to prevent reflections. We only saw Paul use a blunt
spatula and old green kitchen scourer. Obviously the finished
casting cannot be better than the wax model so this
stage is painstaking. Paul was working on a life-sized
torso. The wax was sturdy and did not need support but
there were peculiar ragged holes in the back walls.
One of the beauties of the lost wax method lies in the ease
of connecting cut outs by wax sprues as well as attaching
larger wax pathways which the molten bronze will follow
during casting. The wax model looks like a peculiar insect
with random appendages at this stage.
We went out to the casting room, which was delightfully
warm on such a cold day. However on a hot day temperatures
may reach well over 45°C.
Now a ceramic shell (investment) is made which completely
surrounds the wax (inside and out). We were told
that this involves at least eight dips whilst the model is
spun. Now we could see the reason for the holes cut in the
wax mould as they allow the ceramic core to form. Nails
hold the inner and outer shells together. These shells are
light and strong but, even so, vulnerable places are reinforced
with chicken wire. There is a cup like structure at
the top connected to several larger diameter wax sprues
where molten bronze will be poured in and fed to all parts
of the model.
Normally the foundry only casts once a week but they did
a special one for us.
First the inverted assembly is heated in a gas-fired kiln.
During this time the wax mould and sprues melt and run
out. The temperature is carefully controlled so that the
molten wax can be collected for re-use rather than burn
The hot assembly was put the right way up into a metal
tank and propped up using stones ready to receive the
molten alloy. The foundry prefers to use gun-metal (85%
copper; 5% tin; 5% lead; 5% trace elements) but can make
casting in other alloys (e.g. spelter, a lead/zinc alloy) if
Bronze ingots, which weigh about 20lb, are melted in a
plumbago (graphite) crucible. Graphite is particularly
suitable, as it gets stronger as it gets hotter. The temperature of the casting metal has to be between 1000°C and
1200°C. Although optical pyrometry could be used to
measure the temperature a quick rough and ready cheap
alternative is to stick a red-hot iron rod in and if the bronze
does not stick the alloy is hot enough.
The process, once the crucible leaves the furnace, has to
be quick. Two people controlled the crucible using handles
at either end of an iron harness but an overhead gantry
did the lifting controlled by a third who worked pulleys
somewhat akin to rubbing your tummy whilst patting
your head. The bronze must not be allowed to cool too
much as, if it becomes too sticky, it will not flow into all
the cavities in the mould.
First slag was scraped from the top into a pit on the floor.
Then each ceramic assembly was quickly filled. Finally
the almost empty crucible was laid gently at an angle on
the floor to cool.
Cooling was quite rapid. Bits of ceramic seemed to pop
around the tank. This is inevitable as bronze shrinks on
cooling. After about half an hour cooling the ceramic shell
was knocked away with hammer and chisel. We saw a
flattish model (of a womens back) appearing. It turns out
that flat shapes are difficult to cast, as the mould tends to
be slightly flexible. Philip pointed out imperfections
running across but was not concerned.
Separating the casting from the investment is a good job
for an apprentice as it is carried out in the yard whatever
the weather. It might be unskilled but it is very important
to remove every last bit of ceramic from the core as subsequent
treatments include acid etching.
Back inside again we went to see the next stage in tidying
up the casting called chasing. All sprues are removed and
any traces of them obliterated. The pieces are welded together
and the joins filled. Full advantage is taken of the
excellent malleability of bronze to fill small holes simply
by hammering with a steel tool to slide metal about.
Sometimes the bronze is a little thin where the moulds
have flexed so more can be welded in. The judgement of
the craftsman is all-important at this stage. For instance we
saw specific areas (knee and elbow of a prone body) being
worked on to highlight them.
At this stage the casting is a beautiful golden colour but it
is vulnerable to corrosion. If left in London the casting
would turn black and, indeed, some bronze statues have
been painted black to avoid extra labour. At the seaside
the copper content leads to green corrosion.
The idea of the patination process is to accelerate corrosion
according to the sculptors wishes. There are various
treatments: potassium sulfate leads to a black finish, ammonium
chloride with potash gives a green finish and iron
III nitrate gives an attractive brown. Treatment with a
bismuth salt leads to a rather curious white finish. However
once again the craftsmans touch is all-important. For
instance none of the finished artefacts we saw were a
bland flat colour but all had highlighted areas.
Many famous sculptors brought their sculptures to the Art
Bronze Foundry. If you have been to Kings Lynn you may
have seen Vancouvers statue and in Westerham there is
Winston Churchill. Epstein and Finck are two of the more
famous sculptors who brought their models to the Foundry.
There was a Bafta bronze on the table. It is quite
heavy so it is likely that a less dense material has replaced
the original bronze judging by the ease with which recipients
wave their masks around at the awards ceremony.
The Art Bronze Foundry is eighty years old. The Foundry,
whilst using traditional methods, readily uses modern
materials. Silicon rubber moulds, which can be reused,
have replaced gelatine negatives. The investment used to
be made from bulky grog and plaster but, in the same way
that plaster casts protecting broken bones have become
thinner whilst retaining strength, these new shells are thin,
light and strong. The turn round from original model to finished article is
less than a week. This brings it own problems; the Foundry
is dependent on a regular supply of customers to keep
the plant operating.
Bill Hayter carefully explained legal aspects. The sculptor
owns the original and may specify that the moulds can be
used a certain number of times, say six. However it is
unlikely that all six bronzes will be made at the same time.
The foundry stores the moulds and when the sculptor has
found a buyer he requests another casting. When the specified
number has been made the mould is destroyed. Apparently
this has not stopped a third party (an institution
that should have known better) from requesting their own
casting on the side but this is unacceptable.
When bronzes are sold the dimensions are carefully recorded.
This cuts out the possibility of forgeries by making
a new mould from a bronze. There are three stages at
which shrinkage occurs so any forgeries made from that
positive will be too small.
It is interesting to speculate when a bronze becomes a
work of art. We all know that a painting by Claude
Lorraine for instance is worth much more than a copy
made by a pupil. But casting a bronze involves input by
craftsmen as well as the designer and their work is an
integral part of the finished article. The intellectual property
holder has the original idea and produces the original,
which is unlikely to have the nuances such as depth of
colour of the finished bronze casting but they will have
been consulted at each stage and signed the bronze.
(Although it has been known for this to be done in house
when the sculptor has sufficient confidence in the foundry.)
I would like to record our thanks to the team at The Art
Bronze Foundry for making us so welcome and going to
such trouble to give us an insight into the history and development
of casting bronzes.
Return to Top of Page
The Crags of Sussex: Ardingly Sandstone led by Gareth George,
followed by Identification of Tombstones at Fletching
1 April 2006
Article to follow
Return to Top of Page
Teaching the Dynamic Earth
A demonstration of geomodels for teaching Earth Science.
Set up by Paul Grant and delivered by Nikki Edwards.
18 May 2006
Instead of our usual Thursday evening talk, we invited
Paul Grant to come and give us a demonstration
of the Earth Science Teaching models developed
by ESTA (Earth Science Teachers Association)
and the Earth Science Education Unit at Keele
University. Paul had whetted our appetite by showing
us a video clip of his model of mountain-building
processes when he talked to us about the Baetics
In the event Paul was called away at short notice to
accompany Imperial College students to the Baetics
so he sent along Nikki Edwards to guide us through
Paul had brought along the models a few days before 6 big boxes and
a gutter pipe. It was all very exciting and setting it up with my
colleague Jill Darrell and Nikki was a bit like opening up a Christmas
stocking. Nikki has her own models and unpacking Pauls produced a few
surprises for her: Jill was despatched for some extra bits of kit.
And so the session began. As an ice-breaker we sat in groups and arranged rock specimens at appropriate
positions in the rock cycle. Then in our groups
we were launched to play with the activities on offer.
Laurie spent most of the time repeatedly applying
heat to a small piece of granite and dunking it in cold
water and managed to destroy it. Several of us had
fun with the gutter. It was half-filled with sand then
tilted up so that we could pour water from the top
which overflowed into a bucket at the base. We
each selected a monopoly house and placed it where
we thought it would best withstand the melting glacier
from above. I cant remember who won but I
know mine, strategically placed near the top at one
side, was moved down slope almost immediately. I
think the winner about the only one not to move -
was situated on a stable island within the braids. So
our group moved on to the activity that had sparked
off the session: alternating layers of flour and sand in
a Ferrero Rocher box. An exact-fitting piece of wood
acted as a slab-push force and low and behold our
mountain acquired exotic folds and even a fault. I
think it was Wilf we watched blow down a straw into
a complicated arrangement of chemistry equipment
to cause an oil-well blow-out, although Nikki was
disappointed that no-one got completely soaked!
Apparently this activity is very popular with kids.
Finally Nikki brought out and demonstrated the piece
de resistance: a wax volcano. It worked spectacularly!
A layer of red wax was placed under a layer of
sand in a glass beaker and then both were covered
by water. The wax was gently heated from the base.
Low and behold, the sand rose up and red lava
flowed down the sides at the top and also produced
feeder tubes to the ground surface where it spread
out evenly. It was even slightly explosive at one
Unfortunately we were all having such a good time
that no-one had the presence of mind to take photographs
but details of the models are on their website:
www.earthscienceeducation.com with moving images
of the wax lava. The teachers amongst us
were all enthusiastic about taking the ideas back to
the classroom and newcomers to S260 will have
gained insight into the basic principles of several
geo-processes. For those who were unable to come
but could also find the models useful in the classroom,
an INSET sessions is offered to schools free
of charge, except for travel and refreshment for the
team member who facilitates the course, thanks to
sponsorship of the UK Offshore Operators Associations.
Details are on the website.
Many thanks to Paul Grand and Nikki Edwards for
such an exciting evening which will additionally be
very useful to quite a few of us. Also thanks to Jill
Darrell for her muscle power enabling the models to
be safely installed.
Return to Top of Page
Visit to the Natural History Museum
Earth Science Library
15 June 2006
The Earth Science library were kind enough to offer
two London Branch members the opportunity to take
a tour round the library facilities at the Natural History
Museum in order to promote the wide range of
material and services they have available to outside
organisations and members of the public.
Jenny Parry and I were delighted to take them up on
their offer to view some fantastic books, maps and
works of art, both ancient and modern.
We started our tour in the main Earth Science Library.
If you have visited the Natural History Museum
you may have noticed its inconspicuous entrance
opposite the Ordnance Survey Shop on the
ground floor of the Earth Science building. The staff
had displayed some of the fantastic material held in
the library. This included twelve 3-dimensional
wooden models of geological structures created by
Thomas Sopwith (1803 1879), which were designed
to help geologists and engineers to understand
formations. The blocks are approximately ten
centimetres square and individual strata are depicted
using different colours/types of wood which produces
a most fascinating and beautiful finished
piece. They were often used in universities and colleges
as teaching aids for map-work and structural
geology, what a shame we do not have the opportunity
to use such wonderful pieces of art as study
materials today. We also viewed some unique books
by George Cuvier (1769 1832), the Rev William
Buckland (1784 1856), Thomas Burnett (1635
1715), and a beautiful illustrated work by John Fullwood
(1854 1931) entitled Rocks and Minerals,
chiefly from the South East Coast of England, an
album of 122 pencil drawings and watercolours,
these were just beautiful and unbelievably realistic.
We were then shown up to the fourth floor of the Palaeontological building where we were shown the
special collections and the map room. There are
three special collections rooms, palaeontology, mineralogy
and the John Murray library (John Murray
was the naturalist on the HMS Challenger expedition
(1872 76), this collection was donated with the
wishes that it was to be kept together).
Most of the material in these rooms pre-dates 1850
and is available for viewing by special request. Here
we were privileged to view some unique pieces; the
diaries and letters from the HMS Challenger expedition;
A reference book by James Sowerby (1757
1822) containing some beautiful drawings of minerals,
the staff had been kind enough to also retrieve
the original specimen of Sulfur (kept at the museum)
that Sowerby used as the source of his illustration;
The series of twenty-one sets (355) photomicrographs
of snowflakes by Wilson A. Bentley The
Snowflake Man (1865 1931). Bentley was the first
person to photograph a single snowflake crystal in
1885 and was the first to make the discovery that no
two snowflakes are alike. The pictures were taken
during the winters 1885 1889 in Vermont, USA.
He captured 5000 snowflakes in his life leading to
him being affectionately known as Snowflake Bentley.
On our return to the main library we were allowed
more time to view some of the other works on display,
this included the Geological evidences of the
antiquity of man (1873) by Sir Charles Lyell (1797
1875). Also some beautiful works of dinosaur art
by Neave Parker (1910 1961), Henry de la Beche
(1796 1855), and Thomas Hawkins (1810 1889),
many of the specimens of reptiles that inspired his
artwork were collected in Somerset and Dorset, and
a beautiful watercolour by Sir William Hamilton
(1730 1803) of an eruption at Campi Phlegraei
We also had a chance to see the oldest book in the
Earth Sciences library De Re Metallica (1556) by Georgius Agrcola (1494 1555), the title translates
as On the nature of metals, however this had a much wider meaning at the time and encompassed
any mineral. Finally I have to mention The worlds
mineral masterpieces (2002) by Eberhard Equit
(1939 ®). Who is apparently widely regarded as
being one of the finest contemporary mineral artists
in the world, and you only have to look at this amazing
volume to see why. I strongly recommend taking
a look. A selection of his work can be viewed online
at www.minrec.org follow the art museum link and
select the artist from the list.
A big thank you to all the staff of the Earth Science
Library who were most helpful and approachable, I
hope this brief round-up of a wonderful visit will
inspire some of you to take up the opportunity to
view some of the wonderful archives available. You
can access the library catalogue online at
www.nhm.ac.uk or you
can visit the library by appointment (48 hours notice
required), contact the library staff.
Return to Top of Page
Geology of the Vale of Wardour, The SW Wiltshire Anticline
17 June 2006
On a very hot Saturday morning we assembled in the village of Dinton with our guide Lesley Dunlop. Lesley introduced herself disarmingly, to those of us who did not already know her, as primarily a hard-rock geologist. However, we were very much in sedimentary territory and were
going to perform a traverse of a section across the SW
Wiltshire anticline, the axis of which ran by the river to the
south of the village. We would start by walking to the north,
and then walk back south (and a detour a little to the west)
across the core of the anticline, and then follow the section
in reverse order on the other side.
After appropriate warnings about the need to drink plenty of
water in the hot weather, we set off through the picture-postcard village of Dinton, and then climbed a steep hill
along a sunken lane, appropriately called "Steep Hollow".
To the beginner in geology, a steep climb uphill away from
the core of an anticline might seem counter-intuitive, but in
fact "reverse topology" is commonly found. The upfolding
of the rocks in an anticline causes a weakness, which results in more rapid erosion at the core of the anticline. That
same weakness is exploited by rivers, as here, to create a
We paused near the top and viewed the outcrop by Upper
Greensand exposed on the sides of the sunken lane. This was characteristically
green from the glauconite contained in it
and there was also a lot of iron in the rock, which was not
particularly well cemented and contained a lot of fine muddy
grains. There was much cross-stratification in the lower
part of the exposure near a springline. There was also a
distinctive shell-bed, and there was some discussion as to
the large number of rather broken-up fossils contained in it.
Some thought that the fossils looked like Gryphaea be-
cause of their shape, but this could not be what they were,
as Gryphaea is a Jurassic fossil, and here we were clearly
in the Cretaceous. The consensus was that the fossils were
However, subsequent research carried out by Di Clements
in the Natural History Museum collections established that
they were in fact bivalves, of the species Pycnodonte
vesiculosus. They are also so identified, specifically in
relation to this location, by Isobel Geddes in her book on
Lesley invited us to measure the dip of the rock
(approximately 10° to the North, although the road itself was
dipping to the south, following the reverse topology). We then walked up to the crossroads at the top of the ridge
from which a chalk landscape was visible to the north.
Here Lesley discussed what we had been seeing. The
Upper Greensand was approximately 100 million years old.
The glauconite and the fossils indicated a shallow marine
environment, below the tidemark. Lesley also explained the
broader context of the sequence of sedimentary rocks in
the anticline, which had been folded and tilted after deposition, by the Alpine Orogeny, and then eroded.
While listening to this the writer was at this point bitten on
the finger by a horsefly, which occasioned some discomfort
in the following week. Future visitors to the location are
advised to bring insect repellent.
We then walked back downhill towards Dinton past a quarry
at which we paused briefly. Here the rock was paler due to
leaching, with iron nodules.
As we came back down towards the village, Lesley pointed
out a change in slope as the road levelled off. At the point
where the slope changed clay was seen to be exposed in a
field by the side of the road. Lesley indicated that the flat
level of the village indicated that it was lying on clay at this
point. There was then a slight rise again. Re-entering the
village and posing a wall on a building to one side we noticed a mixture of harder rocks from the locality, blocks of
Greensand with shells, a greyer fossiliferous rock and
some whiter carbonate rock. We passed a large new-style
country house with an inscription proclaiming it to be
"Wright's Manor", built in Chilmark Stone, a creamy variety
of Portlandian stone used in Salisbury Cathedral, with a
slate roof. It was noted that the stonemasons had inserted
blocks of stone upside down into the wall. We then came to
St Mary's church. This had some bits of Greensand in its
construction, quite a lot of material from the Purbeck beds
and a more blocky rock, like Chilmark, probably quarried
very locally. Underlying us were now Jurassic beds of the
Portland and Purbeck . Lesley said that there was a
marked unconformity below the Lower Greensand. Some thirty to forty years of
deposition were missing, having been probably
eroded away early in the Cretaceous.
Leaving the village and turning a bit to the west, we crossed
parkland, passing a lake. The parkland belonged to
Philipps House, a National Trust Property built in 1817 on a
Greensand ridge to the north- east which commanded a
view down to the river Nadder. We crossed a road and
then a field and passed through a spinney to a spot near
the railway where we paused for lunch.
During lunch Lesley pointed that we were close to the core
of the anticline. Here several fault lines ran. There were
parallel fault systems running east-west, and the river utilised the weaknesses to lay its course. Lesley also pointed
out that many of the anticline features were asymmetrical,
the northern part (the side away from the direction of thrust)
There was also some discussion over lunch about a fault
running parallel to and on the south side of the anticline
axis. This was thought to be a deep Mesozoic tension fault,
one of a number in the area associated with the first opening of the Atlantic in the early Jurassic or earlier extension
in the late Palaeozoic as an eastward extension of the
Variscan Orogeny, now deeply buried. This may have controlled subsequent deposition and folding. Initially these
faults were down-throwing to the south, and may have
caused much thicker deposition of Jurassic sediments
down a fault scarp to the south. The direction of movement
or faults such as those would then have been reversed at
the time of the compression due to the Alpine orogeny, so
as to cause a down-throw to the north. Therefore although
the impetus came from elsewhere, much of the movement
in this area would have been on the ancient faults, which in
this case may have contributed to the asymmetry of the
anticline. The movement of the crust during the Alpine
orogeny would also have caused a number of minor tension faults to open up which are found here trending in a
After lunch, Lesley invited us to examine the loose material
lying exposed on a bare patch of the field where we had
stopped. This proved to be of varied origin, iron nodules
from the Greensand, flints from the chalk, shelly limestones
and laminated Purbeck material.
Moving across the railway (and crossing the core of the
anticline) we came down to the river, passing an elegant
hamlet with an old mill house. We followed along a path
bordered by barbed wire and nettles, but then had to leave
it passing under the barbed wire, the party losing some of
its style and dignity for a moment in the process!
We could see that the ground over which we were passing
was partly alluvial , partly limestone. We were over the
Jurassic. Crossing the river, we came up across a ploughed
field containing laminated Purbeck stones, but on the upper and southern side there were numerous flints. Lesley
observed that the River Nadder had probably cut down
further after the deposition of the flints on the southern side
of the field.
Passing along the top of the field there appeared to be
significant amounts of clinker, thought to be from a limestone kiln , and then one of the party picked up a piece of
what seemed to be carboniferous limestone, rather than the
more recent Jurassic limestone we had been seeing. An
animated discussion ensued about this, which was cut short
when some one consulted the OS map and pointed out that
we were walking along the course of a dismantled railway.
What we had been looking at was in all probability remnants of the ballast!
Moving south, we skirted a fenced-off wooded area, and
passed into a spinney through which ran a track. There
we paused, to consider where we were in the succession.
It was felt that we had now climbed up beyond the Purbeck
and Lower Greensand beds and the ground was suggestive of Greensand, perhaps Upper Greensand. In that case
where was the Gault? It was speculated that this was due
to a fault. However, in retrospect, given that our passage
through Dinton suggested that there was an extensive
deposition of Gault in the area, it is probable that our initial
assessment may have been mistaken. Passing along the
track, we did in fact come upon Bog Pepper, just before a
break of slope, which indicated a clay substrate. We
reached Ford Lane, walked along it a short way and then
most of us followed the steep track up to Fir Hill. A few of
the less energetic of us stayed behind.
On the way up, we passed a second exposure of Upper
Greensand, which contained a fossil bed very similar to that
at the top of Steep Hollow above Dinton. We examined this
more closely on the way down, but before proceeding took
the dip of the Upper Greensand at that point. It was approximately 5° to the South. We continued up to the top of
Fir Hill where there was a reservoir and from this point the
Chalkland of Fovant Down was visible further to the south.
On the Down, military units which had encamped there in
the past had carved out their regimental badges into the
Chalk. Some of us had seen those badges that morning on
the drive over to Dinton.
It was felt that the structure of the anticline had been convincingly demonstrated.
Summing up, Lesley said that the Vale of Wardour provided
a good illustration of an Alpine anticline, like that found in
the Weald, but in a much smaller area and with a more
extensive series of rocks exposed, because the core went
down into the Jurassic. It was well worth revisiting if some
of us should be again in the area.
We then walked back downhill and crossing the river returned to Dinton and the cars. Then, after a pause for appropriate refreshment at a local hostelry, we returned to London.
With thanks to Kim Vignitchouk for her photographs
Return to Top of Page
Shetland led by Allan Fraser
31 July - 7 August 2006
Article to follow
Return to Top of Page
A Novice Eye View of a Trip to Harwich and Wrabness, Essex
7 October 2006
Article to follow
Return to Top of Page