• Blown glass is an art that dates back to the Roman era. It is the process of taking hot, molten glass and using a blower and other tools to create pieces that have been blown into their shape. Blown glass has distinct characteristics that are not found on machine molded and pressed glass pieces.
  
  

Pontil or Rod Marks

• A pontil or rod mark is where the pipe was attached to the glass during the process of blowing the glass. Pontil marks may be found on the bottom of bottles and vases, on the stem or side of glasses or on the bottom or side of bowls. A pontil mark may look like a circular indent on a piece or a bulge on others. Handblown glass will always have a pontil or rod mark; however, they may be hard to find. For example, pontil marks are hidden on lamps and other display pieces, a search covering the entire piece is necessary to make sure that it is truly blown glass.
  
  

Color Streaks

• Color streaks may be present in blown glass pieces, this is especially true when the piece has been made from recycled and a combination of glasses. The streaks appear due to the melting process and the colors of glass used. For example, a dark green glass piece, may have light green or even blue streaks of color running through the glass.
  
  

Slight Variations

• Handblown glass will have very slight imperfections or variations in shape. There are artists who can make almost completely symmetrical pieces; however, these pieces still will not be precision identical, as is seen with machine molded pieces. Look for wavy marks in the piece, a slightly irregular shape or if one piece is slightly smaller than the matching piece.
  
  

Seamless

• Blown glass pieces are seamless. There will be no lines running down the piece where two pieces of glass met inside a manufacturer's mold. Look to make sure there are not raised areas where two pieces of glass came together. A handblown glass piece will be one continues piece of glass. Also, the inside of the pieces will not be completely smooth, but the outside will be.
  
  

Bubbles

• Bubbles can appear in handblown glass. This is due to air becoming trapped in the molten glass during the blowing process. Some handblown pieces will have only a few bubbles throughout, while others can have hundreds, depending on the type of glass blowing that is being done. However, watch for manufacturers who now add bubbles to their pieces. Look for the bubbles in conjunction with other handblown glass characteristics to make sure that it is authentic.