British Colour Standard

Glass blowing is by definition a hot process! The transformation of raw materials into glass takes place at around 1,320 °C / 2,400 °F, and the glass emits enough heat to appear almost white hot.
The glass is then left to "fine out" (allowing the bubbles to rise out of the mass) and then the working temperature is reduced in the furnace to around 1,090 °C (2,000 °F).

So much work goes into each piece. All bubbles & forms do vary a little, as is only fitting for somehing that is crafted in this way.