how can you tell if a vase is authentic handblown Venetian glass?

Answer 1

It is very hard to tell if a vase is Venetian, specifically Venetian glass tends to be very much larger, and certain colors, techniques or marks tend to be there but it takes an expert to tell this unless the piece is really large. Current Venetian style takes pride in being able to handle large and heavy work.

It is usually easy to tell if the work is hand blown however because you cannot just take a hand blown piece off the blow pipe, but must put on a pontil (punty) that is a bit of hot glass on a steel rod.

At that time the part of the piece that was attached to the blow pipe can be done but then it has to come off the pontil, This leaves a bit of broken glass on the bottom.

Most Venetian glass has this bottom piece ground and polished off, but some older pieces and certain houses take pride in the mark and only keep any sharp edges off.

In either case it will show as no matter how perfectly polished, it is still different from fresh glass. A machine blown piece will not have any such mark, except in very rare instances when a special gadget is used instead of a pontil on some footed pieces.

Another give away is when it is the rim of the vase that is ground and polished thus eliminating the need for a pontil.