Unlike antique and collectible pottery which usually has a stamped or incised mark on the bottom, antique and vintage glass oftentimes does not. This makes identifying glass pieces a challenge, but not impossible.

Antique glass takes in a wide variety of different types of glass and glassware made over centuries of time. It includes everything from elegant glass and signed art glass pieces to Ball canning jars, medicine bottles, and other utilitarian items made of glass.

Glass manufacturers have been making countless pieces of glass in numerous styles and designs since the start of the Industrial Revolution. Many glass manufacturers and patterns are well known, such as Rosepoint by Cambridge Glass Company, Adam by the Jeannette Glass Company or the Silhouette glass stemware of the Libby Glass Company. Others are much more obscure such as Tiffany pastel glass, Butterfly and Floral by the Roden Brothers of Montreal or Beaded Shell Pressed Glass by the Dugan Glass Company.

Although many antique glass pieces are unmarked, there are a great number of pieces that do have one or more of four glass markings and can be identified—trademark, logo, symbol, and signature.

Most often a glass mark is on the bottom of the piece, but there are some pieces that are marked on the side. Sometimes a mark has faded over time and using a magnifying glass or a jeweler's lope in good lighting may be necessary to see it.

A piece of antique glass will often show structural clues to its age. The pontil on the bottom of a piece of glass indicates that it was blown rather than molded. A piece made in a mold will show a mark all around it from where the two halves of the mold met.

An antique glass piece may also exhibit bubbles, indicating poor blowing or molding techniques.

If a piece of antique glass has a glass mark or logo that isn’t familiar, the best way to identify it is by using a glass marks identification guide or a glass price and identification guide. However, many of these identification guides cover just one type of glass, such as carnival glass or depression glass.

Identifying Antique Glass with Clues
Most pieces of antique glass don’t have any markings. But there are other ways to help with identification. Check for excessive wear and scratches on the bottom. If the piece is gilded, it may show signs of wear.

Many times a glassmakers used a type of mark known as an acid badge. Many pieces of glass from the mid 19th century onwards have registration numbers. Earlier pieces may have a diamond mark to show that the glassmaker registered his design.

Often when an artist signed a piece of engraved glass, he made his signature very small and part of the design. After 1905, it became common to sign cut glass pieces as companies tried to protect their patterns from being copied.

Glassware with a stopper, such as a perfume bottle or a decanter, from the 1800s and 1900s should have matching numbers on the stopper and the bottle. Often the numbers were scratched on the stopper's peg and the bottle's neck.

Antique glass markings help solve the mystery of the old glass piece's past and provide clues for identification, value and authenticity.

Learning the “Feel” of Antique Glass
Old glass and new glass feel different. Begin by learning what new glass feels like. When holding a drinking glass or vase feel the weight, color, translucency etc. In learning what modern glass looks and feels like it’s easier to make distinctions between new and old glass. The difference is even more evident when handling brilliant cut glass. Older cut glass is vey sharp while newer cut glass is smoother. And he surface of pressed glass, which often imitates cut glass, is always smooth and has a thin raised line running completely around it where the halves of the mold used to make it came together.

Characteristics of Antique Glass
Even if a piece of antique glass has no mark or signature, there are other ways to identify its age.

Chips can be damaging to the value of a piece of glass. They can be felt and have depth to them. The size of the piece of the glass and the size of the chip will affect the value of the piece. Feel the chips—new chips will be sharp while old chips are often smoothed at the edges over time.

Cracks are more difficult to find. Take the glass piece out into the sunlight to look for any hairline cracks that cannot be seen with indoor lighting. Unfortunately, cracks drastically reduce the value of a piece.

Flaking usually occurs around the rim of a piece of old glass. A flake is small flat, thin piece of glass, but it doesn’t affect the value of the piece.

Nicks are missing pinhead size pieces of glass which don’t affect the value of the piece. Though the piece won’t be mint, it won’t be considered damage, depending on the age of the piece.

Rough Spots or Areas can be identified by running a finger along the rim or base of a drinking glass or goblet.

Scratches, often an indicator of age, hide on the bottom of a piece of antique glass. They typically go in every direction on an older piece while those on a newer one will all be going in the same direction. This is particularly evident on reproduction pieces.

Straw Marks are considered irregularities in old glass when looking at it from the side.

Wear to Gilt can be seen on the rims or bases of older glasses.

It’s best to er on the side of caution when purchasing older pieces of glass. As with pottery and porcelain, newer pieces of glass can be made using older molds. But the composition of the glass will be different, making it weigh less.

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