The Age of the Bottle While not all old bottles are valuable, an older bottle is more likely to be worth more than a newer one. Seams and pontil marks are two of the ways you can determine a bottles age. The pontil mark is the mark at the bottom of the bottle where it was attached to the glass blowers pontil rod.

What is antique blue glass called?

Cobalt glass Cobalt glass—known as smalt when ground as a pigment—is a deep blue coloured glass prepared by including a cobalt compound, typically cobalt oxide or cobalt carbonate, in a glass melt.

How can you tell if glass is blue?

Look for any type of glassware, vase, flask or jar that has a blue appearance. These are all considered to be cobalt glass. Some glass will be entirely blue, while other pieces may have a striated blue appearance. It is also common for the glass to have white swirled along with the blue.

What color of depression glass is most valuable?

Pink glass is most valuable, followed by blue and green. Rare colors such as tangerine and lavender are also worth more than common colors like yellow and amber.

What is the most rare depression glass?

Royal Lace (1934–1941) The most sought after pattern of Depression glass is arguably Royal Lace, which was made by the Hazel-Atlas Glass Company. This pattern was manufactured in green, pink, crystal, and most notably, cobalt blue.