Hi Wombly Anne
Lovely piece. It's Murano definately.
These are called "Geodes" because of the resemblence to mineral geodes which get struck in half to reveal the treasures within.
They were made by several Murano firms, but this opaque style is relavively unusual and Archimede Seguso was making them in opaque colors in 1958 according to Pina Italian Glass.
Another possibility is Vistosi who (unusually) used balck and white glass as well as taking the genre forward to sliced stone-like paperweights. No date is given on the particular example shown.
There could well be others. The master glassblowers , Maestri changed companies regularly and took their techniques and designs with them. Copying would also have been rife. Murano is small, people know each other, workshops would mpost of have had doors and windows open.
So it could be hard to pin down for sure.
the rim chips do affect value considerably as it is the simplicity of form which gives these pieces their modernist appeal but not not even 99p this must rate as a mega bargain and I hope you get much pleasure from it.
As to the technique that can't have been easy. As noted in the Repairs thread, the different expansion and contraction rates of different colors can cause all sorts of serious problems. See that thread for more info.