Mirrors have a long history in myth and fact. Though the first mirrors may have been no more than still pools of water, their development soon progressed to polished metal and mercury-backed glass, according to online design newsletter Designboom. The modern mirror-making technique of chemically coating glass with silver (now often aluminum) was invented in 1835 by the German Justus Von Liebig in 1835, said Designboom. With careful examination and a little historical knowledge, the time period of any glass mirror can be determined.
Measure the mirror. The size will tell some of its history. According to Basic Antiques online, mirrors were never more than 2 feet before the 1800s.
Determine the frame style. Framing followed the furniture styles of any period. This will determine a time line of production. The date of a mirror can be estimated by the style. Framing evolves from wood to plaster and composition boarding.
Assess the mirror's shape and setting. Painting and painted panels can serve to distinguish historical placement . Old wood veneers were thicker and not uniform as they are today.
Look for any trademarks or other determining marks, labels and dates.
Remove a screw from the back of the mirror. Irregular threads or head on the screw signal older age.
Look at the thickness of the glass. Old glass was thin and had a gray look to it. It was wavy and did not cast an accurate reflection. Thicker glass means more recent production.
Check the edge of the glass. Older pressed or poured glass has a rounded appearance while cut glass will have a crisp edge. Also look at the interior of the glass from the edge vantage point. The newer cut glass will appear smooth and have a clear consistency throughout while older glass will have some pits or small nicked indentations.