BCD 2017

T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 7 127 METAL, WOOD & GLASS 3.3 (roughly 300–1800mm), such as panelling, boards, shingles, laths, staves and pins. Hardwoods cleave best radially, conferring the added advantages of reducing moisture- related movement and enhancing the aesthetic qualities of oak by exposing the maximum amount of the attractive medullary rays on the wide face. In contrast, softwoods such as Scots Pine cleave best tangentially. This can often be seen in nailed-on, imported Georgian laths where a face knot runs through a series of adjoining laths. Hewing is the technique of using edge tools to ‘square up’ logs, although the final shapes are often rectangular in cross-section as well as tapering along their length. Due to the adaptability of the axe and the hewer, cranked or curved timbers present no particular problems. Whatever the shape required, lines are first snapped on to the log, the bark being either left on or removed. Two different types of axe are used – firstly the scoring axe, which is often the same axe that was used to throw the tree over. The log is supported on low bearers or trestles and held-fast with pointed iron dogs. The long-handled, double-bevelled scoring axe first chops a series of notches into the log at roughly 300–400mm intervals. Then the same axe is used to strike off the timber between the notches and to clean off any remaining large irregularities. This leaves rough-hewn surfaces consisting of shallow notches, torn-out grain and axe-marks that are then cleaned up with a second type of axe, which is generally shorter handled, single-bevelled and slightly convex. It is used to remove just the final shavings, to get exactly down to the line. The final surface finish is defined by the slightly undulating, smoothly cut surface with some small amount of tear-out on one side of any knots. The quality of some hewing from the 13th and 14th centuries has to be seen to be believed – it can appear almost hand-planed, so crisp are the corners and so smooth is the surface. In theory, no trace of the rough- hewing should be visible, but in practice it becomes increasingly evident on hewn timber surfaces from the 15th to the 19th centuries. Hewing was practised widely and nearly all buildings with structural timbers have some visible hewn surfaces. With imported softwoods, which mainly date from the 17th century onwards, the hewn baulks show a similar, slightly undulating, smoothly cut surface finish. Hewing is slower than cleaving but quicker than sawing. Sawing shows the most variation of the three types of conversion due to the different ways the saw can be presented to the timber and the motive power driving it. Sawing appears around the end of the 12th century in the form of ‘see-sawing’, where the hewn timber is inclined at an angle and supported at about mid-length on a single trestle. The frame saw then cuts from one end down to the trestle, before being withdrawn. The timber is then pivoted on the trestle like a see-saw and a second cut started from the other end. Bearing in mind the steel technology available between the 13th and the 15th centuries, it is a testament to the skill of the saw-makers and sawyers that these two cuts almost always line up. Close inspection reveals that the saw-cuts do not quite intersect but that this last connecting piece of timber is cleft off, leaving a torn surface in the shape of an equilateral triangle about midway along. See-sawing is also distinguished by the orientation of the saw marks at an angle of about 50–70° to the length of the timber. Between the end of the 14th century and the mid-16th century, a new technique was Cleft surface: the process of splitting tears the grain apart and leaves a distinctive, slightly ridged finish. See-sawn surface: inspection of the area where the two saw-cuts intersect shows that the last connecting piece of timber is cleft off, leaving a torn surface midway along in the shape of an equilateral triangle. Pit sawn surface: the finish is characterised by saw-marks at about 75 to 85° to the length of the timber and a cleave-off at one end in the shape of an irregular triangle. Mill sawn surface: wind or water-powered reciprocating saw blades cut at about 90° to the length of the timber, leaving evenly and closely spaced saw marks with no cleave off. gradually adopted across the country which consisted of supporting the hewn timber horizontally, either over a pit or on high trestles, and sawing from one end only. This technique is often generically described as ‘pit sawing’ and from the 17th century onwards it used a saw without a frame (a whip saw or pit saw). Pit-sawn timber is distinguished by saw-marks at about 75–85° to the length of the timber and a cleave-off at one end of the timber in the shape of an irregular triangle. Evidence of mill sawing by European sawmills is mainly found on imported Baltic softwoods from the 17th century onwards. Mill sawing used wind or water-powered reciprocating saw blades which cut at about 90° to the length of the timber, leaving evenly and closely spaced saw marks with no cleave off. It can be difficult to distinguish between mill sawing and good quality pit sawing. Circular sawn timber arrived in the late 18th or early 19th century and became established with the advent of steam power during the 19th century. It is easily identified by its very distinctive, large, curved sawmarks radiating across the surface. Lastly, bandsawn timber dates from after the 1860s and can be recognised by sawmarks that are at 90° to the length of the timber but with a regular pattern of more widely spaced sawmarks than timber from reciprocating sawmills. CONVERSION PRODUCTS The following types of conversion are often encountered; the first three types were extensively used to produce a variety of timber products including posts, ties, plates and rafters: Boxed heart or boxed timbers have just the outside of the log removed and so tend to be roughly square in section. They can be