If you think it is very old have you find bits and pieces in the metal.
Hi , I think this quote is a little misleading , yes finding bits and pieces in the metal can be an indication of its age but should not be relied upon ,this would depend on the quality of the metal and the objects being produced , i have in my collection many glasses from the early 18thc and the 17thc , made form very fine metal both lead and soda that are as clear and imperfection free as any later produced glass , the quality of the metal is what determines whether an early produced glass can be called a very fine specimine or a run of the mill glass produced for the mass market , many items were produced for the very top of the market using the finest metals and in the hands of the best blowers have produced some of the finest glasswares known , these being the most desireable to modern day collectors of early glass , and as such will command the highest of prices , ie a heavy baluster glass of lesser metal and made by a less competent hand will be valued far lower that a glass made from the finest metals pruduced by the highest skilled blowers.
I can also add that a flat polished foot though not common can also be found in very early glass ,I have seen and owned a few large early 18th glasses with very large thick feet that have been flat ground possibly due to the large size of the pontil resulting in a rocking glass,these being produced before the norm of polishing out pontils leaving a coin polish mark,
Having said all that though I am not trying to argue that your glass is any earlier , i would still say that it is more than likely late 19thc , or as Ming says possibly edwardian .
Hope i havn't rambled on too much