Blown glass is handmade with care by an artisan, and thanks to this craftsmanship, collectors and buyers value it more than mass-produced glass. Glass blowers create their works of art by blowing into the open end of a rod that has hot glass on the opposite end. The way the artists blows through the rod and turns it affects the design, so no two pieces are exactly alike. Sometimes blown glass is easy to spot; other times it's more difficult. Several clues can help you tell if a vase is blown glass.
Look for the Maker
Because glass blowing is an art, most blowers will sign or mark their works. Look for the artist's mark or signature or a company mark on the bottom, under a handle or in another inconspicuous part of the vase. A marked piece of glass generally denotes an artistic element that's not common in molded glass, however the mark alone is not enough to determine whether or not you have a blown glass vase. For example, artists who paint on mass-produced vases may also mark or sign their work.
Examine the Handle and Seams
Take a close look at the vase. If it has a handle, can you tell where it was added onto the piece? In the case of molded glass, the handle is often part of the mold and shows a seamless attachment to the base of the vase. If you can tell where the handle has been added to the base, it may be made from blown glass.
Blown glass may have other seams too. Artists may blow sections and piece them together. Finding seams in a glass vase does not necessarily rule it out as blown glass.
Look at the Lip and Base
Check the lip of the vase for a pinched area. A small pinched area around the lip of a vase indicates the spot where blown glass is removed from the blowing tube. Finding a pinched area at the lip or opening of the vase is a good indicator of blown glass.
Instead of a pinched area, you may find what appears to be a scar or a swirl on the bottom of the base. In this case, the vase was separated at the base instead of the top of the rod. The scar is called a pontil mark and is another indicator of blown glass.
Perfect symmetry is a sign of molded glass. As artisans know, it is very difficult to make an object that is perfect and the same is true with glass blowing. If the vase is perfectly symmetrical, it is not blown glass. No two blown glass vases will be exactly alike.
Bubbles can appear in both blown and molded glass vases. Bubbles in blown glass will not be consistent in color or size. Blown glass will also capture various strands of colors. Bubbles and colors in molded glass will appear more uniform.