All About Blown Glass

A Glassware Technique Perfected by the Roman Empire

Tiffany Silver Overlay Vase with Polished Pontil

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The technique for mouth-blown glass was perfected before the rise of the Roman Empire and grew in popularity while the Roman civilization flourished. The mouth blowing technique (also known as free-blowing) has been used to create glass around the world for centuries. The process includes blowing short bursts of air into a molten glass which is gathered at one end of a glass crafter’s tool known as a blowpipe.

Is All Blown Glass Mouth Blown?

No, blown glass can also be made by machine with an air compressor and many companies that produced glassware widely collected today employed this technique, as do contemporary glassmakers handcrafting decorative glass. Some of the most famous glass of this type has been produced by renowned artist Dale Chihuly, whose colorful glass can be viewed in the lobby of the Bellagio hotel in Las Vegas, Nevada.

Chihuly Garden and Glass in Seattle
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Is Blown Glass Ever Molded?

Yes, blown glass can be formed with the aid of a mold. Fostoria is one of the major companies known to expertly craft elegant glass that was uniform in shape using this technique for many years. This type of ware will not have signs of being molded in the true sense, however, as described below.

The Difference Between Blown and Molded Glass

The first thing to look for on blown glass is a pontil mark (as further described below). Whether it's rough on the bottom or smoothed out, all blown glass will have this feature. Molded glass, which is the same as pressed glass, will not have a pontil mark on the bottom, and it will have mold seams present somewhere on the piece. The mold seams are usually found on the sides of glass where the parts of a glass mold fit together whether in two or three parts.  

What Is a Pontil Mark on Blown Glass?

Quite simply, a pontil mark is the spot on the bottom of a piece of blown glass where the rod used during manufacture was broken off after the piece was completed. Some pieces of blown glass will have a very rough pontil, others will have a rather lumpy pontil that has been partially finished by reheating the glass and smoothing it.

Pontil marks are key indicators that glassware was made by blowing rather than pressing it into a mold. A piece might be mold-blown with the aid of machinery, or mouth-blown by a single craftsman, but if a pontil mark is present the glass was blown in some fashion rather than pressed.

Some marks of this nature are very rough and look like a break in the glass. Others exhibit a mound so you can tell that area was reheated and smoothed out by the person manufacturing the piece. The type of pontil mark often reflects how nicely the piece is manufactured overall, but not always. You still have to look at the other details of the piece like symmetry and the presence of debris in the glass to evaluate overall quality.

One thing is for certain, the best pieces of glass will rarely have an ugly pontil mark on the bottom. Finely crafted blown glass including art glass and elegant glass will have what is called a polished pontil. This means the pontil has been polished completely smooth leaving a round or oval indention in its place on the bottom of the piece. A polished pontil is a sign of meticulous detail in the manufacture of quality blown glass.

Pontil soaking in the molten glass
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Does Blown Glass Ever Contain Ash or Other Debris?

Yes, blown glass can contain debris. However, the high-quality collectible blown glass will be free of these types of imperfections. They would be considered flaws in art glass or elegant glass made by the best companies.

Is Mouth-Blown Glass a Lost Art?

No, skilled crafters mouth blowing glass, like those working at the Jamestown Glasshouse in Jamestown, Virginia, form objects without the aid of a mold as they’ve done there since the early 1600s when the colony was first settled. Other artisans across the globe are still mouth blowing glass as well, and some of them have exhibitions to share their craft with others. 

People at a glass factory
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