Furniture Detective: Screws give valuable clues when in search of antique furniture origins

One of the most overlooked and least understood clues in establishing the date and authenticity of older and antique furniture is the story that screws can tell about the history of a piece.

Screws are relative newcomers to the production of furniture, primarily because they are so hard to make by hand. But as the complexity and sophistication of furniture increased in the late 17th century and the use of brass hardware, locks and concealed hinges became more popular, there was an obvious need for a fastener that could hold two surfaces together without having to penetrate the back surface of the second piece.

The screw on the left was handmade in the late 18th century. Note the flat spot on the shaft, the irregular threads, blunt tip and the off center slot. The screw in the center is machine made around 1830. It has sharp, even threads, a cylindrical shape, blunt end and the slot is still off center. The screw on the right is a modern gimlet screw, post 1848, with tapered shaft, even threads, pointed tip and centered slot. Photo courtesy Fred Taylor.

The handmade nails of the period derived much of their holding power from the ability to drive the nail through two surfaces and bend it over on the back side, i.e. “clinch” it tight. But that solution would not work for securing the top on a chest of drawers or table top without either driving a nail through the top from above or clinching it on the top to hold it fast.

The same problem arose while trying to affix a lock to the back side of a drawer. For a nail to hold, it would have had to be driven through the front of the drawer. The same was true for hinges used under a table leaf.

The concept of the screw is an ancient one. Archimedes, the Greek scholar and mathematician of the third century B.C., used a shaft with a surrounding spiral in a tube to lift water, making use of one of the basic tools of physics – the ramp. In effect a screw is a ramp wrapped around a column.

But how to manufacture that ramp on that column by hand? They were seldom attempted in quantity much before the William and Mary era, but the sophistication of that period required the use of more screws so the process became more widespread.

Handmade screws of the 18th century started out much as the handmade nails of the period did, as square iron nail stock produced in a rolling mill. In the Colonies, these iron rolling mills existed all along the Atlantic coastline, turning out nail stock for the blacksmiths and “nailers” in the growing settlements. In many cases the same smith who made the nails occasionally turned his craft to the making of screws and thereby left us with personal traces of the maker.

The smith heated the square stock and then began the process of pounding out a round shaft. In this process, “round” was a relative term since very few hand hammered objects of iron are perfectly round. When a suitable degree of “roundness” was achieved, the hot shaft was jammed into a form on the anvil, similar to the swage block used in making the hammered head of the rose head nail. But the form used for the screw was a more or less round shallow depression into which the top of the shaft was hammered flat, producing a screw head. The slot for the bladed screwdriver was cut with a hacksaw.

So far so good. We’ve got the column and the head but what about the ramp, also known as the worm or the threads? Lacking a cold hardened steel die with which to cut the thread, the craftsman had to cut it himself by hand. This was usually done in laborious fashion with a file. When the smith had the length he thought was needed for the job, he simply cut or snipped the threaded shaft.

This entire hand-done process leaves a multitude of clues on the handmade screw, just waiting for our inspection. Starting with the top of the screw, the head, evidence of handwork is abundant. In most cases the head is not perfectly round and is not centered perfectly on the shaft. The hand cut slot is seldom perfectly centered on the off-center head. Below the head, on the smooth portion of the shaft above the threads, is the most likely place to find areas that still show a flat side of the original iron nail stock. This portion of the shaft is almost never totally round or totally smooth.

This article originally appeared in Antique Trader magazine

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But the most obvious clue to the handwork is the thread. The pitch, the angle of the thread to the shaft, will vary considerably from thread to thread as will the depth of the cut into the shaft that produces the thread.

The edges are often flat since they were filed into shape, and the tip is invariably blunt since the smith just cut it off. And the overall shape of the entire screw is cylindrical rather than tapered, as is the case in modern screws. Because of the individual nuances and variables in the handwork process, no two handmade screws are identical.

Screws with these characteristics were produced until early in the 19th century. Around 1812 a machine was introduced that made screws on a lathe but the War of 1812 slowed its distribution and development. After the War, the new machine went right to work, turning out virtually identical screws with sharp even threads, but the heads still had to be hand forged and the slots were still cut with a hacksaw, producing slight variations caused by this last bit of handwork.

These new machine-made screws also resembled their ancestors in that they were still almost perfectly cylindrical and had a blunt tip.

The introduction in 1848 of the completely machine-made gimlet screw, with a tapered shaft and a pointed tip, marked the beginning of the modern era in screw production.

With the exception of the materials used and the various types of heads, Phillips, Torx, square recess, etc., the basic design of the screw has remained unchanged since the mid-19th century.

Examine examples of old screws very carefully and they will provide you with a valuable clue to their origin and perhaps to the origin of the furniture in which they are found.

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