- Bricks & Brass: House Dating Tool
- Researching Historic Buildings in the British Isles
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Walk around almost any town and look at the brickwork you pass. Often it can tell you something about the building and the area where it stands, about the purpose for which it was built and how that has changed over the years, and even the status of the building's original owner. In town centres especially, look up above the shop fronts where you can see the original fabric of the buildings, before they were mauled by the makers of gaudy modern shop fronts.
Sadly, as with so much else, modern buildings are becoming homgenised, with the same bricks and the same styles being used in towns all over the country, but even so, after several decades of uninspired building, brickwork is once again being used imaginatively to help to enrich our townscapes. Have you ever thought why a brick is like it is? Its size is mainly determined by what a brickie can pick up in one hand, and keep on doing so for several hours. Over the centuries, the size of bricks has changed quite a lot, and until a few decades ago, bricks in different parts of the country tended to be of different sizes and proportions.
That harks back to the 18th century brick tax, which made it more economical to use very large bricks rather than smaller bricks. You can often see joints in walls where bricks of different size meet. There is an example in the pictures below. An extreme response to the brick tax came from Joseph Wilkes, who doubled the thickness of bricks made at his works at Measham. These monster bricks became known as 'Jumbies' or 'Wilkes' Gobbs''. You can see them alongside normal thickness bricks in the pictures below. It is often assumed that the desire to avoid the brick also stimulated the use of brick tiles — wall tiles that looked like bricks but weren't.
You can see face and end view in the pictures below. Brick tiles' had been introduced much earlier as a way to clad timber buildings and give them the appearance of brick, and they were also taxed during most of the period when bricks were. With the increasing use of timber frames in modern buildings, brick tiles are again being used to provide a more traditional appearance than other cladding such as plain tiles.
See more detail, analysis, diagrams, pictures and maps ,. Prior to the age of mass transport, buildings in different parts of the country mostly used local materials, including bricks made from the local clay. So bricks in one part of the country would have a very different colour and texture from those in another, giving buildings a distinctive regional look and feel.
That changed when cheap transport began to favour mass production in areas where the bricks could be made more cheaply, and transported more or less anywhere. This section of is not yet fully developed, but there are a couple of examples in the pictures below. The way the bricks fit together in a wall is called the bond. It forms the visible pattern that you see on the wall. The ability to spot different bonds while walking around a town, and the realisation that they could tell me something about the history of the building, was what first got me interested in brickwork.
It's a bit like learning to recognise different types of tree or different bird. FIrst you just learn to give them names, then you learn more about them, and why they are as they are. Buildings make a public statement that can reflect the owner's perceived status. Over the years fashions change but the desire to be in fashion, and the desire for quality by those who could afford it, persisted.
So did the desire to project the appearance of quality by those who could not afford it but would like it thought that they could. Each method has a distinct role in the investigation of historic buildings. None is infallible and before embarking on an extensive dating survey, due thought must be given to what might be achieved and which methods might be the more successful. If necessary, seek advice. Whilst earlier types of wooden joints may be copied in later buildings and earlier styles may be reintroduced in later periods to confound the conservationist or historian, any reuse of older materials should become obvious by the use of the chronometrical methods described here.
The incorporation of ancient bog oak into a building, no matter how intricately carved or jointed, would immediately become obvious to the chronologist, as would timber renovations. Dendrochronology is the oldest method, having been introduced over a century ago by an American astronomer, Professor A E Douglass. He wanted to know whether the number of sunspots affected weather on Earth. If this were so, the width of the annual growth rings would show changes in synchronism with the sunspot numbers. He established a laboratory in the university of Arizona, at Tucson, to study tree-rings.
Unfortunately, after many years of analysis he was not able to confirm the correlation he sought.
Bricks & Brass: House Dating Tool
Nevertheless, the laboratory was able to demonstrate many interesting properties of ring widths and their relationship with various aspects of climate and other natural phenomena and, of course, their use in the accurate dating of timber. His laboratory is still one of the leading centres in world dendrochronology.
It was not until that the science was taken seriously in Europe, mainly through the efforts of Professor Huber in Germany, and not until after World War II that such studies became established in the UK. The main centres in Britain researching this field are located at universities in Belfast, Cambridge, East Anglia, London, Nottingham and Sheffield with several freelance practitioners.
Whilst most dendrochronological research is still concerned with climatic change, where the precise dating provided by the growth rings is of vital importance, all units in this country are proficient in performing dendrochronological surveys of buildings. Oak is the species of prime interest and it is possible to date wood back to over 7, years with a precision, in appropriate circumstances, of a single year. This is most impressive and makes dendrochronology the main dating method for structures containing oak timber. The method relies upon the response of trees to the weather during the growing season, which runs from March to October.
In a 'good' growing season the trees within a large climatically homogeneous region all respond by putting on a wide growth ring within the cambium which separates the sapwood from the bark. In a 'poor' growing season the trees all respond so that only a very narrow growth ring is formed. In more typical growing seasons a ring of intermediate width is produced. It should be noted that there is no direct linear relationship between ring width and, say, sunshine, or other weather components Thus a 'good' or 'poor' growing season is defined with reference to the amount of growth produced.
For example, the year had a gloriously hot, long summer with most rainfall arriving in autumn but the trees did not appreciate it and all oaks produced a distinctively narrow ring. Again the summer of was cold and wet, quite different from , yet the trees also produced a distinctly narrow growth ring. So it will be seen that seasons that are hot and dry as well as those that are cold and wet will produce a narrow ring so that such a ring is not diagnostic of the weather.
Year by year the trees throughout the region produce a similar pattern of wide and narrow rings in response to the weather changes. It is this pattern that allows the accurate dating. The pattern of ring widths on a specimen taken from a building is matched, using a computer with a 'master chronology' often several centuries long for the particular area.
This regional chronology will have been painstakingly built up from many thousands of measurements and by cross-matching many overlapping patterns of timbers.
Researching Historic Buildings in the British Isles
The youngest patterns are obtained from living trees, where the felling date of the final ring is known. Progressively older patterns are obtained from trees in recent buildings, older buildings, archaeological sites and ancient bog oaks. Because of local, non-climatic causes of change of growth width, the chronologies around the country vary somewhat, and the best dating match is always obtained from a local regional master chronology.
The dendro-date is thus the year in which the final ring of the specimen grew the year in which the tree was felled, but not necessarily the year in which the building was constructed. In order to obtain an accurate match and hence a date, it is important to have at least 80 rings on the specimen that is to he dated. With fewer rings the pattern might have repeat matches at different points in the time scale and so give rise to multiple possible dates.
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This has implications for some vernacular structures in which rapidly grown, wide-ringed oaks, 30 to 40 years old, were used. In such instances it might be possible to date the wall plate which often contains far more rings.
In practice it is found that or growth rings are most likely to provide a unique match. However, because of the local ecological, non-climatic effects on the tree ring, it is not possible to guarantee that any particular specimen will give a date. In order to have greater certainty it is important to obtain several samples, in the form of cores drilled from the timber, and to construct a 'site chronology' for the building. The number of cores required will depend upon the complexity of the structure, but some ten cores per building phase is preferred. These are normally taken by the dendrochronologist in co-operation with the historian and the position of the cores is carefully marked on the building plan for future analysis of the results.
The core leaves a small hole in the timber of about 15mm in diameter which may be plugged with a timber dowel. Although this method is capable of dating to the individual year, in practice several factors conspire to reduce the precision in dating the construction, sometimes drastically, and it is important to be aware of the limitations. Whilst in the middle ages it was the practice to use the timber 'green' - usually within a year of the felling date - in more recent times the timber is usually allowed to dry out, sometimes for decades, before use.
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Furthermore, carpenters, aware of the effects of insect attacks, would deliberately remove the sapwood and even some heartwood. The number of sapwood rings may vary between 15 and 50 years, depending on the position in and the age of the tree. Thus the year of the last ring dated could be misleading to the construction date and be underestimated by an unknown number, possibly 60 years. Sapwood may be found on at least some of the timbers in the dendrochronological survey and the site master chronology will lead to a more reliable date than an individual core.
Whereas tree-ring dating is limited in this country to oak structures, radiocarbon dating may be used for any wood species and, indeed, for any other organic based materials found in buildings such as: The range of radiocarbon dating reaches back to 60, years. For the last few thousand years it can have a precision of a few decades and may, in certain circumstances, be comparable with tree-ring dates. The laboratory at Cambridge here in England was among the first six to be set up anywhere in the world.