A Collector’s Guide to Mirrors
by George Read
First Published as "Mirror, Mirror", in Southern Accents, Time-Warner Publications
The modern mirror, as opposed to the cloudy, spotted, grayish-glass based reflecting device that preceded it, was invented in Venice, in about 1504.
Glass, the most obvious necessity for a mirror, has been around since about 4 bc. The Ancient Egyptians made multicolored beads and small vessels of it, and the Greeks and Romans after them produced glass objects, especially drinking glasses, of great sophistication. You can buy a two thousand year old Roman drinking glass at auction for a few hundred dollars, and often less. They have a beautifully iridescent surface from their years underground, and it is hard to believe they are not broken.
The Search for Clarity
Practically every innovation and technique in glass-making that we know today had been investigated and mastered by the year 1 ad. The one important exception was clarity. The secret of making clear glass evaded the efforts of the world's glassmakers for nearly five millennia.
These early civilizations had mirrors of a sort. They were small concave plates of murky glass about the size of tea saucers, which were backed with thin sheets of rolled lead. We are generous in calling them mirrors. All of these early efforts suffered from poor-quality glass and an unstable backing. They reflected the world with the same sort of image we see now in our reflections at the bottom of a polished silver tray, or in a pool of still water.
The discovery by Venetian glassmakers of a formula for clear, colorless glass was a triumph. Their crystalline glass was free of bubbles and distortions and, most important of all, it was virtually free of color. Only two other known substances were thought then to equal the first examples of Venetian glass as a symbol of divine purity, the finest white quartz and diamonds. The Italians, always superb marketers, described their cooled glass as "celestially pure."
Protecting the secret
The Venetian Doges recognized the value of the discovery immediately, and took steps to safeguard the formula. They forbade anyone, including apprentices, in the glassmaking industry to travel outside the confines of the Republic, and declared the new formula a protected secret of the Republic. Divulging the formula was punishable by death. This was effective. The Venetians created and protected a virtual monopoly on crystal glass that lasted for about 150 years.
They solved the second problem, a suitable backing for the glass, a few years later. Heated, liquefied tin mixed with mercury formed a reflective amalgam that spread thinly and evenly, adhered beautifully to the plate, and reflected an image without spotting or discoloration. This silvery amalgam also resisted tarnishing, as both silver and lead had done in the past.
By about 1510, the formula was complete and the mirror was born. The first examples came from only one place, Venice, and they were rare and expensive. A moderately-sized mirror cost the rough equivalent of about $50,000 in today's currency.
The old Venetian monopoly on crystal glass still ranks as one of the most lucrative Europe has ever known. As the industry flourished, the factories in the city burned with such constancy that Venetians feared an accident in one of the kilns that would incinerate the city. The glass factories were moved out to an island in the lagoon, Murano, where the damage might be contained.
The Formula Escapes
The secret eventually leaked out, first to the East, where Bohemian glass factories began to rival those of Murano, then to Germany, France, and England. Louis XIV eventually cracked the international monopoly. His Hall of Mirrors at Versailles was both a show of opulence and a declaration to the world that French glass had arrived. The mirrors at Versailles were all products of the French glassworks at St. Gobains, and they were equal to the crystal of Murano.
The basic techniques of glassmaking remained virtually the same for the next 300 years. We learned to make larger panes in the 18th and 19th centuries, but it was not until the second quarter of the last century that the industry developed the ability to make enormous plates of strong, clear, undistorted glass. This breakthrough in technology gave architects the means to design the glass and steel buildings that are now commonplace in modern cities.
About the Gilding
Re-gilding an antique mirror frame does not detract from its value. As long as the new gilding is of good quality, and the frame does not look "dipped", or over-gilded, re-gilding is a common and acceptable restoration.
Constant re-gilding of mirrors, picture frames, and other furniture was common practice through the 18th and 19th centuries. So it is nearly impossible to tell when gilding is "original.” It is certainly possible to see that gilding is old and well-patinated, however. The presence of fine old gilding adds significantly to the value of a mirror, as much as 30-50%.
Mirrors From Picture Frames
Picture frames are often made into mirrors. These pieces usually appear too boxy, or too square in shape. A picture frame converted into a mirror has generally less than one-half the value of a true mirror. These pieces always have new glass, of course.
Replaced glass in an antique mirror frame does not detract significantly from its value, provided the new glass is not visually jarring or too modern looking. However, original glass in a mirror adds to its value, sometimes by as much as 25-50%. Re-silvering of a mirror glass that has deteriorated beyond reasonable use is not advisable. Collectors should simply remove the old glass, store it, and fit the frame with a good replacement.
Old glass is very thin, seldom exceeding 3/16 of an inch. Modern glass is 1/4-3/8” thick, nearly double that of old glass. Thickness can be tested by holding a coin or business card to the surface of the mirror. The distance between the reflection and the coin is the thickness of the plate. A coin tapped on old glass gives a sharp tinny ring. Modern, thicker glass resounds with a dull, muted sound.
Old glass is less pure than modern glass (usually from a high lead content) and it reflects a slightly yellow or grey tone. Modern glass is completely colorless. Hold a white business card to the mirror to see the true color of the glass. If the color of the reflection matches the color of the original, the glass is Victorian or later. If the reflection is yellow or blue in tone, the glass is probably old.
The silvering on old mirrors was poured on to the center of the mirror-backs and then blotting out towards the edges. The plate was then set on a tilt and the excess was allowed to run off the low end. This took a few days. So old silvering differs in thickness from the center to the outside edges, and from top to bottom. When this silvering breaks down, it does so unevenly. Modern mirrors that have been treated to look old are usually distressed evenly.
Characteristics of Forgeries
The backs of old mirrors will nearly always show several sets of empty screw holes. These tell-tale sign of older attachments are nearly always present in old mirrors.
Many mirror plates were given a beveled edge. All beveling done before about 1850 is irregular and very soft-edged. This beveling was done by hand with a pumice stone. Old beveling is clearly visible to the eye, but the edge is so soft that it can barely be felt with the fingertips. Modern beveling is done by machine and it has a sharp, hard edge, which is a good indication of replaced glass.
It is rare to find a delicately-carved mirror frame with no breakage. Finely-carved decoration on chair splats, the galleries of tables, and in other fragile areas should have been cracked or broken at some point due to common use. Most have some evidence of repair or replacement. Perfect condition in a delicate mirror is often a characteristic of modern work, or a forgery.