Look for labels. Antique furniture, 100 years old or older, will not have a label. Some very old pieces may have a handwritten name in black pencil. Pieces built before the 1930s will have labels that are rather crudely printed on plain paper and glued to the piece. Such labels will be extremely yellowed with age and very brittle, and the maker may be identified as the Acme "Comp.," meaning "company." Furniture built from the 1930s to the 1950s will have labels that are more "slickly" printed, less yellowed and less brittle, and the firm will be listed as Acme "Co.," the modern abbreviation of "company." Modern furniture will have "glossy" labels, containing a company name ending with "Inc." Incorporation is a more modern invention and a dead giveaway.
Look for joint methods. Truly antique furniture will have non-uniform joints, especially where two panels of a drawer come together in a "dovetail" pattern. They will look hand-carved. Furniture made with machines from the 1950s onward will tend to have perfectly uniform dovetailing. Older dovetailing is usually very complex in shape, while modern dovetailing will have a simpler pattern. Both demonstrate the difference in the use of hand tools versus power tools used to create dovetail joints. Check screw types too: antiques will have matte-finished, flat-head screws, usually dark in color. Modern pieces will have shinier Phillips-head screws.
Examine the type of wood used. Antique furniture before 1900 will be made of solid, usually expensive (now) maple, quarter-sawed oak, cherry, and walnut. Antique furniture was built of hardwoods produced from local timber stands and was built to last by using thicker planes of wood. Furniture made after 1950 is most often made of pine and other cheaper woods that are merely veneered with better woods. Any particleboard use is a giveaway as "modern."
Examine the finish. Antiques are usually finished in waxes or varnish and shellac made with oil. Old varnish and shellac have a yellow tinge and may be crudely "splashed" on the back edges of the piece, evidence of "by hand" work. Almost all antique finishes are oil-based, while modern pieces are finished with water-based products such as latex acrylic. Smell the finish: an oily smell indicates an oil-based product; no odor at all usually means a water-based product.
Examine any "carved" decorations on the piece. Antiques are hand-carved, and the decorations are usually thick and not perfect. Decorations produced after 1930 are machine-made. They will be perfect and identical throughout the piece. The giveaway here is a set of perfectly matched, highly carved knobs: "perfect" means "machine" and probably not antique.