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ISSN 1357-4442Editor: Simon Denison

Issue no 38, October 1998

LETTERS

Shroud dates

From Mr Ian Freeman

Sir: In his latest book on the Turin Shroud, The Blood and the Shroud (Wiedenfeld & Nicolson, 1998), the writer Ian Wilson quotes some work by Dr Leoncio Garza-Valdes, a microbiologist at the Santa Rosa Hospital in San Antonio, Texas.

In this work, Garza-Valdes claims to have discovered a `bioplastic coating' in the fibres of the Shroud, formed by the activity of bacteria and fungi, which could have produced an error in the radiocarbon dating of the Shroud carried out in 1988. Garza-Valdes believes the Shroud really could date from the 1st century, not the 13th century as radiocarbon suggested.

If this claim is well-founded it would, of course, have serious implications for radiocarbon in general, in contexts much wider than the Turin Shroud. Has there been any serious scientific evaluation of Garza-Valdes's work?

Yours sincerely,
IAN FREEMAN
Bedford
31 July

Editor's note: According to the Oxford radiocarbon dating lab, the carbon date of organic material can indeed be affected by later contamination, such as by bacteria and fungi. However, to make a supposedly 2,000-year-old piece of linen appear to be 13th century, huge quantities of modern carbon contamination would be needed - enough to double the weight of the shroud. This seems improbable.

School history

From Mr John Malam

Sir: I refer to Helen Paterson's concerns about `the downplay of history' in primary schools (Letters, July). The `literacy hour' - the Government's proposed extra hour a day devoted to literacy - seems in fact to have provided an unexpected opportunity for history to go to the top of the class.

Some educational publishers now see it as a chance to deliver history as descriptive narrative. Archaeology is well suited to this treatment; and for young children, does it really matter that in the telling, some liberties may be taken, where creative invention fills the gaps that archaeology does not record?

Perhaps what is worrying about the National Curriculum is the lack of British history - prehistory glossed over, much of the medieval period ignored, the industrial period largely avoided, and local history struggles because of the lack of suitable teaching materials.

Yours sincerely,
JOHN MALAM
Winsford, Cheshire
16 July

Underwater work

From Mr Ian Oxley

Sir: I thought your readers might like to know about a long-term project, called `Sea Site', which started this summer and seeks to investigate the deterioration of artefacts underwater.

The project began with in situ studies on four cast iron guns which probably date to the early 19th century. Three were from Aberdeen harbour, and the other was found in the Firth of Forth off Burntisland. The guns were later placed in a redundant, Victorian sea-bathing pool in Cellardyke, Fife, where they can be permanently submerged.

Methods for studying corrosion in situ have been developed by researchers from the Western Australian Maritime Museum over the past 20 years. The routine recording of in situ measurements has been an invaluable tool in understanding the corrosion mechanisms and modes of deterioration of metals on marine archaeological sites. With the aid of such information it is possible to stabilise the object and even start the conservation of iron artefacts on the seabed using sacrificial anodes. This strategy significantly reduces the time and cost of conservation in the laboratory.

The method entails drilling though the surface concretion and corrosion products which encapsulate an iron artefact after it has been submerged in the sea for any length of time. Thereafter the corrosion potential and the surface pH of the metal are measured. The former will indicate whether the artefact is actively corroding, being passified by corrosion products which will slow the corrosion, or is in a stable condition. The pH at the metal surface indicates the acidity resulting from hydrolysis of corrosion products.

It is only relatively recently that this method has been used in Northern Europe. Dr Ian MacLeod from the Western Australian Maritime Museum has assessed the state of preservation of several guns and an anchor from the Duart Point wreck site in the Sound of Mull, and subsequently a series of sacrificial anodes were placed on the objects. A sacrificial anode, normally made of a metal such as a zinc or aluminium alloy, is electrically connected, for example by copper cable, to the artefact which is manufactured from a less reactive metal such as iron. The iron artefact gains protection as the electrons released from the corroding anode flow through the copper wire into the artefact. The artefact is the cathode of a corrosion cell while the seawater completes the circuit. This effectively lowers the corrosion potential and hence the corrosion rate.

The results from Sea Site's initial study showed that the guns were actively corroding in their new environment. Secondly, several people obtained reproducible results illustrating that the equipment and method could be used by non-specialist archaeologists and diving conservators in the future. Later this year further visits to the guns are planned with the aim of taking more measurements and fitting sacrificial anodes to them to slow the rate of corrosion.

Yours sincerely,
IAN OXLEY
Archaeological Diving Unit
University of St Andrews
22 July

Mill dovecotes

From Mr David Whiteley

Sir: The article on dovecotes, `Exploring the round houses of doves' (June) was very interesting, but no mention was made of what we used to call `pigeon lofts' in industrial mill buildings.

The one I know best was in a gable end of the original structure of Pool Paper Mills, Pool, in Wharfedale, near Otley, Yorkshire. My grandfather was one of the founders of the firm BS & W Whiteley, established in these mill premises in 1886. The circular opening still exists, although many newer buildings round about have been demolished. An inscription in the top stone is still partly visible and reads `JM 1762', the `JM' referring to John Milthorpe who was the owner of the farm on whose land the mill was built.

Pigeons were still using the loft until the outbreak of World War II. Then, I remember my father being very upset by a government instruction that all pigeons had to be destroyed in case they were used as carriers, and the openings sealed so that birds could not use them. I wonder if this applied to any of the structures referred to in the article by Klara Spandl.

Yours faithfully,
DAVID H WHITELEY
Harrogate
21 August


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