Mirrors have been in use since the 17th century and have filled both a functional and stylish purpose due to their often-elaborate detailing and framing. While many antique mirrors are now reproduced in more modern materials that can withstand time and use, there are a few ways to determine if a mirror is an authentic antique or a modern reproduction.
Look at the mirror frame. If it is made out of wood, locate a screw someplace not immediately visible, remove it carefully and examine it. Antique screws will be irregular and rough in size and shape because the screws were made by hand. In addition, look at the wood near the hardware. If there is some natural darkening of the wood, the mirror and the hardware are probably all original.
Examine the thickness of the glass, if possible. Modern mirror glass is fairly thin, while the glass used for antique mirrors is thick, heavy and solid. Carefully hold the tip of a metal key to the mirror glass and see how close the reflected image of the key tip is to the actual key. If it is very close, it is more likely that the mirror is an antique. Repeat the same experiment with a modern mirror to get an idea of the distance of the image with modern glass.
Look at any detailing or painting on the mirror frame and examine it for signs of hand-detailing. If the detailing or paint is perfect and completely precise, it was probably done by machine and is a modern reproduction. However, if the details show some irregularities and changes in thickness, the mirror is likely an authentic antique.
Hold the mirror and look at the veneer closely for thickness and irregular sizing, indicating work done by hand. If the mirror is precisely cut with no irregularities, it is more likely that the veneer was manufactured by machine.
Examine the frame for plaster placed on wire, which was a common method in the 19th century. Because plaster is fragile and easily damaged, if the piece is marked as an antique but is in pristine condition, be wary that it may be a reproduction. The chances of a plaster and wire frame, which were called composition frames, making it intact over time with no chips or damage are slight.
Keep an eye out for antique mirrors with two small glass plates that are set next to each other in the frame. These mirrors are indicative of mirrors made in America and Great Britain in the late 1700s and are rare.
Look for mirrors with thinner glass plates with a dark reflection, which is caused by a mercury-coated foil that was placed over the glass during mirror-making in the 18th century.