Hand-forged, stamped and machine-cut iron tacks, pins, wire nails, staples and other hardware such as clips, hooks, clamps, braces, snaps and zips are used to attach layers of upholstery, and support systems to frames.
Eighteenth-century tacks have hand-forged iron shanks and hammered heads sometimes referred to as ‘rose head’. However, this term is also used to describe some machine-made types and should therefore be avoided as confusing. By the late eighteenth century the process had developed further – shanks were machine-cut but the heads were still hammered by hand. It was not until the early nineteenth century that the heads were machine-stamped. Today upholstery tacks are generally blued cut steel and of two types, fine and improved, the latter being slightly heavier with a larger head. They have a small spur of metal used for temporary tacking and can be used with a magnetic tack hammer. Professional upholsterers commonly kept sterilized tacks in the mouth, from where they could be quickly and easily spat onto the magnetic head, temporarily placed and then driven home with the hammer head, thus keeping one hand free to hold material. Clout tacks have burred shanks to increase the anchor into the wood. Gimp pins are small thin nails, enamelled or lacquered in a range of colours, that are used to attach gimp braid, fringes and exposed backs of outer covers. They were known in the late eighteenth century as copper pin nails. Today they are generally of fine cut steel. Small wire nails have been used for the same purpose.
Since mechanization in the closing years of the eighteenth century, tacks have become plentiful and comparatively cheap. More are therefore used in so-called traditional upholstery as currently practised than were used in preindustrial age furniture and this may cause more damage to the frame. It is a common misconception that traditional upholstery (using hand-built industrial age upholstery techniques) is more authentic and less damaging to the frame than modern application techniques. Staples properly delivered from electric or pneumatic guns probably cause less stress to the frame than tacks hammered in by hand, though the staple is used by most manufacturers of commercial furniture for reasons of economy. Also, modern techniques usually involve the application of a complete preformed unit which only requires the application of a single row of metal fasteners to secure it to the frame. This contrasts with hand-built techniques where each separate layer of the multilayered structure is attached to the frame with a separate row of metal fasteners. Metal fasteners are available in a variety of sizes, gauges and metals.
Standard sizes of wire from which commercially available fasteners are derived conform to certain recognized gauges (e.g. Birmingham Wire Gauge), but this differs internationally (e.g. metric, Imperial, USA). Some are plated either for decorative purposes or to increase their resistance to corrosion. Generally speaking, the larger tacks and staples are used to hold webbing, the smallest and finest to hold the top cover. Metals include iron, steel and copper alloys. Close examination of tacks and nails may indicate the type of manufacturing process. Features to look for include tapered and non-tapered shanks, uniform sizes and shapes, surface burrs and striations, gripper die marks and metal type. These features may indicate techniques of manufacture and may suggest a date. For example, uniform sizes with flashes may suggest casting whilst identical features may indicate machine manufacture.