A maker's signature is one way to authenticate an antique. For furniture, this could be a brand on the underside, a paper manufacturer's label secured to the piece or a name written or signed in chalk, pencil or ink in an inconspicuous place such as a drawer bottom. A potter's name or initials may be incised into stoneware. On glass, ceramics and metal, look for identifying marks on the bottom.
Documents that prove the provenance (origin or history) of an antique can authenticate and add value to the piece. These documents can include wills, letters, diaries, historic records and photographs that describe the item and place it at some fixed point in history.
Take the reputation of the antiques dealer into consideration. Is he or she experienced and well-regarded in the antiques trade? Is he or she a member of a national antique dealer's association such as CINOA, Antiques Dealers' Association of America, or National Antique and Art Dealers Association of America? If so, he or she is unlikely to misrepresent a reproduction as an authentic antique.
If you have serious doubts about an antique, scientific high-tech methods to authenticate age and manufacture methods include X-rays, CT scans, microscopy and ultraviolet and infrared analysis. But be careful how you handle the antique; in order to keep its value, it must be cared for properly.