What is Alum?
Alum is a double sulphate of aluminium sulphate with either potassium or ammonium sulphate. It can be found naturally occurring in some parts of the world but not in Britain. In this country alum has to be processed from shales or clay that contain pyritiferous material. In the medieval period alum was very important to a number of industries. It was used as a mordant for fixing natural dyes in materials. In papermaking it acted as an adhesive to bind paper fibres. In the tanning process it was used to increase the suppleness of leather. It also had medicinal properties. In earlier times it had to be imported from Spain, Turkey or North Africa. In the 16th century growing problems of supply and the break with Rome led to Britain searching for local sources from which to process alum.
The Island Connection
The Isle of Wight's connection with alum production rests on only three pieces of evidence: the place name, patents issued during Elizabeth I's reign and a reference by Sir Richard Worsley in his 18th century history of the Island. A map of c1590 shows the area now known as Alum Bay was called 'Whytfylde Chine'. In 1562 a certain William Kendall was given a patent for exclusive rights to search for alum in the southern counties, including the Island. Worsley reproduces the warrant but there is no record of Kendall actually exercising his right. Nevertheless it's unlikely that Alum Bay would be so named without some sort of works there. What is known of alum works elsewhere on the south coast suggests they were quite short lived operations, so it's possible the Island works also had a brief life. The main problem in the south was the lack of fuel, which was required in copious amounts to calcine the shales or clay. The lignite at Alum Bay was probably used but it was a poor fuel, giving off too much smoke. It was the fuel shortage that eventually drove alum working further north. By the beginning of the 17th century alum shales discovered in the East Riding of Yorkshire could take advantage of the Yorkshire coalfields.
The Local Seams
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We cannot be sure of where alum was extracted at Alum Bay. There are three recognisable 'clusters' of layers which have the potential to produce alum. These are noticeable dark grey or black areas that occur in three locations of the Bracklesham beds. The clays smell strongly of sulphur and in some places a yellow efflorescence is visible. It seems the most likely layer from which alum was produced is the lower (far right) of the three areas where, in the darker grey clay, pyrites and carbonaceous matter are evident. It's possible that an experimental alum works was set up on a ledge at the foot of the cliff and is now long gone. |
. . . and One Strange Reference
In a book on 'English Industries in the Middle Ages' [Salzmann c1910] the author quotes the Bristol clothing trade in 1346 referring to 'Alum de Wyght'. If indeed this refers to alum from the Island in the 14th century it would confound all other historical data. Either Alum Bay had a sophisticated processing works centuries ahead of its time, or it had naturally occurring alum. Both seem unlikely. One possible explanation is a misinterpretation of the quote. In some trades alum was technically known as 'white stuff'. Still, it makes you wonder . . .
June 1999
See subsequent developments in History Centre news item of December 2000
The History and Geology of the Needles Park