The Furniture Restorer Who Can Date a Chair by Its Joinery

Adam Bowett, one of Britain's leading furniture historians and practising restorer, can determine a chair's approximate date of manufacture within a decade by examining its joinery alone, without reference to style, timber, or surface finish. The type of joint, its execution, and the tools used form a chronological signature as reliable as a hallmark.

The evolution of chair joinery follows technological and economic pressures. Seventeenth-century chairs used through-mortise-and-tenon joints secured by wooden pegs, borrowed from timber framing. The joints are robust, often over-engineered, and the peg holes are typically offset to draw the joint tight, a detail called drawboring.

By the early eighteenth century, chairmakers adopted blind mortise-and-tenon joints. The change reflects improved glue technology and the influence of Dutch and French design favouring cleaner lines. The mortises of this period show the scalloped bottom left by a brace and bit, a distinctive tool signature.

The introduction of the mortising machine in the mid-nineteenth century produced joints with flat, uniform bottoms and parallel sides immediately distinguishable from hand-cut work. Machine-cut tenons show circular saw marks rather than the rippled surface of a hand tenon saw.

Dowel joints appeared from the 1840s, offering faster assembly at reduced strength. The presence of dowels in a chair claiming to be eighteenth century is an immediate red flag. Screw and bolt joints indicate twentieth-century production, with thread pitch and head type narrowing the date range further.

Screws narrow the date further. Hand-filed screws, made before about 1760, have irregular threads, blunt ends and slots noticeably off-centre, because the slot was cut with a hacksaw after the head was formed. Lathe-cut screws from the later eighteenth century are more regular but still blunt-ended; the sharp gimlet point only arrives in the 1840s. A blunt screw with a wandering slot fits a Georgian chair. A pointed one does not, whatever the catalogue says.

Two further tells sit on surfaces nobody bothered to finish. Look at the underside of a seat rail for saw marks: a pit saw leaves straight, slightly angled parallel lines, a circular saw leaves arcs, a band saw leaves straight vertical ones. Then measure a turned leg in two directions. Timber shrinks across the grain and barely along it, so an old turning is measurably oval; a perfectly round section on a supposedly Georgian chair is a modern replacement.

Repairs matter as much as originality. Animal glue softens with heat and moisture, so a joint made with it can be taken apart, cleaned and re-glued indefinitely, which is why conservators still use hide glue and why a chair mended with PVA, or worse with screws driven through a mortise, has lost both value and its future. Having a frame properly knocked apart and re-glued runs to a few hundred pounds; undoing a bad repair costs more.

When evaluating antique chairs, examine joinery before surface. Turn the chair over, look at the underside, and if possible inspect a joint. The joinery tells truth that refinishing may have obscured. A genuine eighteenth-century chair with original joinery is significantly more valuable than a restyled Victorian piece. Study at https://www.furniturehistorysociety.org