Welcome to t-net. I can't tell from your picture, but are there bubbles in the glass? The furnaces from before the early 20th were not able to control the heat well and this often resulted in bubbles in the glass. Also, is there a pontil mark on the bottom? A pontil mark is the mark left over from the glass blowing process. When the glass blower is done, he had to break it off from the tube that was holding the object in the fire. This will leave an obvious mark called a "pontil". However, before you get all excited about it's antiquity, I'm reminded of an incident where I got all excited about a bottle at my girlfriend's house, until she told she made it in a crafts course at the local university. In other words, old technology can be easily reproduced today. Nice bottle though, where did you get it?