So here is the new film about making Hembury type bowls https://www.youtube.com/watch?v=gnKPTq_SGUw&t=516s
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Wednesday 13 January 2021
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Chapter 5 from my dissertation
Chapter 5.
Clays and
soils of Devon.
The sourcing of early southwest Neolithic pottery has depended largely
on identifying inclusions but not the clays. Archaeologists have agreed
generally that local clays would be sourced, not more than 3km, (Gosselain, The
source, accessed on line) for making pots from the site. However, the only
definite way to source clays is to test them through SEM and NAA-Neutron activation
analysis, XRF analysis. These are the normal tests to determine chemical
analyses of clays and archaeological sherds. This produces statistical and
chemical analysis data which is used for a finger print match from samples
taken from sherds, and it has to be considered whether the extra cost of this
type of research is worth the gain in statistical enhancement of the current
state of knowledge. If this information
was available it would be possible to write definitive clay paste recipes for
the Neolithic, not just speculative ones.
The clays and soils are mapped below, in Figs 12 and 13 ((Harries et al
2004 Gallois, 2004) and the maps
are relevant only to the study and prospection areas, of east Devon.
I.
Sampling the clays, quartz and sands.
Appendix II provides a list of the sources of clay and tempers which
were sampled, prior to work starting on the quartz temper project.
Quartz is available within most types of geology of the region. The
quartz used in this project was sourced from The Plym estuary to The River Otter,
at Hams Cottage, Honiton, see Fig.11, and Budleigh Salterton beach and estuary. The
quartz pebbles from Budleigh were very distinctive in their uniform size and
shape, however, and although Budleigh has been cited as the most likely source
(Quinell and Taylor, forthcoming) of
quartz used for pottery from sites in east Devon, pebble beaches are protected
which prevents collection on a large enough scale for a project of this size
when other sources are easily available. Pebble and vein quartz is readily available
on beaches such as Whitsand Bay, nr Plymouth, in the river sands on the River
Otter, Creedy and Yeo. Additionally, vein
quartz is widespread in the environment. It is possible to say that it is found
everywhere. From the samples prospected for the purposes of this project, this
would appear to be the case. A lot of
vein quartz ends-up as river smoothed pebbles of all sizes, both crystalline
and non-crystalline. There are a lot of large, outcrops of crystalline quartz
on Dartmoor both east and west. There are small rounded grains from granite river
sands and Upper Greensand river sands (personal observation). It is also possible to find vein quartz which
contains well-formed crystals.
The geology of the region has featured heavily in this project. The soils and subsoil particularly, not least
for prospecting for good potting clays. As the project has proceeded the geographical
area which should be looked at has increased to include Cornwall. However, when
the focus of the project changed to production
issues where sourcing clays was no longer the focus, the scope and timing of the project have limited the
prospection for Cornish clays within the study area and only small samples of
the east Devon clays have now been collected. I still haven’t managed to find a freely
available source of Permian breccia clay.
The
articles which have been really useful in locating some of these resources are
published by the Ussher Society, Geoscience in the South-West England, which,
among other types of research, run geo-commercial prospecting projects testing
the stability of soils and subsoil in advance of civil engineering works. All
articles are free access and available on online. www.ussher.org.uk. In fact
the Ordnance Survey soil maps have not been referenced as they are not as up to
date now as the Ussher Society proceedings.
The
clays of the Exeter and east Devon region consist generally of the Namurian
clay, which is found all over the region, see Fig 12 above, it is the
weathering product of the shale-slate
beds from the upper carboniferous Crackington formation; as well as the
Devonian red sandstone clays which have not been prospected or used in this project. The Permian breccia, which would probably be
relevant to the Raddon enclosure pottery, formed along a fault in the
Crackington formation in the Permian era which is called the Crediton Trough,
(Harries et al 1995). The Gault or
keuper marl clays which are formed on the Upper Greensand which were sourced at
Branscombe and Monkton, nr Honiton and extend beyond Lyme Regis would, perhaps,
be relevant to the pottery at High peak and Donkey sanctuary.
Fig.11… River Otter at Hams Cottage, Honiton, Devon. Showing the natural
sieving action of sand and gravel on meanders and river banks. Author’s
photograph.
Although
these two clays are very distinct, the Branscombe sample being a much darker
brown, The Monkton Greensand sample is likely to be the same clay type as that
found three kilometres away at Hembury Fort, see fig 13 below,. Hembury is covered in the exact same clay (personal
observation, Todd, 1984)) and both
these clays are weathered in situ. Both
clays are extremely sticky and would likely make goodpotting clays. Initial plasticity tests for these clays was positive. With levigation and sieving, their plasticity can be increased but it
is not definitively possible to say anything about the potential of clay
until it has been fired to temperatures of 800˚, 1000˚,1150˚, 1280˚ Celsius. These are the traditional
temperatures used to determine at which temperature clay matures and if it
melts at any of these temperatures, it is not possible to use beyond that
temperature and thus limits the potential of the clay.
Fig. 12. Geology of east Devon. Showing the major geological formations
and nomenclature. This is the source for naming the yellow clay used in
experiments as Namurian. (Harries et al 2004)
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