Not a new technique really. Roger Angel's work at the UofA in Tucson has been with spinning molten glass to make a mirror. You get the basic figure with the spinning and then you need to finish the glass with standard finishing techniques. The surface of the glass needs to be stressfree and at no more than 5 millionths of an inch from the proper figure. With the technique you have described, you may get to about 2-5 thousandths of an inch of stressed glass if you do a good job. Sorry but it's something that we've been by many times.