The first step is blowing a large 4 gather (dipped in the molten glass 4 times) blank. Colour is applied in the form of condensed coloured glass, which is covered with clear lead crystal. The end result of blowing is a bubble shaped like a very large rugby ball.
This is cooled over night in a kiln and when cold is carved using a diamond saw. Either ends of the rugby ball shape are cut away and smoothed till fine then horizontal slices are cut away on the saw until almost through the wall of the glass leaving very thin contact points between the two sides of the cuts.
Then it is placed in a kiln again and slowly brought up in temperature to a point where the glass is just beginning to move. I take a thick metre long metal rod, cover the end with molten glass and push this onto the hot form till it cools and adheres to the base enough for me to lift the form out of the kiln.
Now on the end of the rod it is introduced back into the red-hot heat of the furnace turning slowly continuously. In the heat the carved parts polish and the thin contact points melt and come apart so that the wave begins to open up. This is repeated several times until the shape is as required and then knocked off the rod (leaving the punty mark) and cooled down overnight once more.
Finally when cool the base is ground and polished.
I developed this reheating and reforming of cut glass while teaching at Sunderland University.