Blown glass can be obtained by blowing melted glass and expanding it until it reaches the exterior shape of the mold. This way the interior of the piece is random, therefore the thicknesses are not even.
Triplex Glass: Using the same technique and blowing three layers of glass, we can so obtain Triplex glass. It’s formed with transparent glass in both interior and exterior layers, and opal glass in the middle layer. The same process could be used for glass of different colors.