There are two ways to handblow Glass, one is of course without a mold, this is usually noticable by the not so perfect shape, They can also blown into a mold, these are perfect form over and over, however for the most part you will still have a seam, usuallly very slight. Then of course you have the ever popular machine blown, which usually has a very distinct seam, and of course they never bother to polish it out, because this is like Libby glass that will be found in the $1.00 store, very visible seam. Usually Art glass has the pontif still rough like your piece, Studio Artist usually don't spent too much time with making the bottom look good, where the Major Art Glass makers with heat and polish the pontif down smooth or almost smooth.