| Glasses are often used to enhance the light and artistry of candles. Frequently these take the form of either a floating candle sitting in liquid, a candle sitting inside of a glass, or a candle poured into the glass itself. The later two may have problems with certain types of glasses.
Flames create convection cells within the container that they are in. This allows for air to come in, get heated up and leave. It is possible to smother a candle in a tube that is too narrow for a convection cell to form. For this reason, champagne flutes and highball glasses would never work well as candle holders. When the candle got part way down it would no longer be able to form the convection cell and fresh air would not be able to reach the flame.
Glasses that are recommended are martini glasses, red wine glasses, old fashioned glasses, mason jars, and pint glasses (but not pilsner style). All of these have a wide mouth and remain wide enough for a candle to comfortably burn. | 
