To determine age, consider the form and function, tool marks, construction techniques, and materials used in the furniture. Pit saws, used from roughly the 1600s to 1750, left irregular, slanted, deep rough marks.
Windsor chairs were not around before the Queen Anne period.
Up-and-down saws left vertical, crisp uniform marks and were used from 1700 to the 1860s.
Probably the easiest to recognize are the curved marks left by the circular saw, circa 1840. The vertical, crisp, uniform marks left by the band saw are not very deep.
Use your fingers on drawer bottoms or backboards of case furniture.
If you can feel slight, parallel ridges and hollows, the piece was hand planed, probably prior to the mid-19th Century.
Construction techniques can assist you in dating furniture. In the 17th Century, butt and rabbet joints were used.Hand-cut dovetails appeared late in that century and for the next 80 years or so, dovetails were wide, stubby, and crude. By the end of the 1700s, dovetails became thin and delicate. If you find Phillips head screws throughout, you don't have an antique. If it is 1/32nd of an inch thick, it is Victorian or newer, as compared to the 17th and 18th Century 1/16" to 1/8" veneers.Mortise and tenon joints were also used in the 18th and early 19th Centuries. On the other hand, hand forged nails and screws with off-center slots and uneven threads can be taken from older furniture and used in a piece made yesterday. Learn to recognize the elements of different furniture styles.The use of square or oblong wooden pins that held in place by the shrinking of the wood was another joinery technique of that time. If you find a piece of furniture that seems to combine several styles, it is most probably not a period piece, but a later reproduction. Are all the parts original, or have there been replacements and repairs? Since wood is an organic material, it shrinks across the grain with age.Scalloped dovetails can be dated to the 1890s and were only used for a short time. You might think it's a modern material, but the Egyptian Pharaohs used laminated wood in furniture and it was used in England in the 1740s. You may not be able to see this with the naked eye, but if you measure a circular table top with the grain and then across the grain, there should be a difference if the table is an antique.Machine cut dovetails were made from the middle of the 1800s onward. Three-ply plywood as we know it today was made in 1905. On turned parts of furniture, such as chair legs, use calipers to take measurements to check for shrinkage.