You can get this unusual look by putting hot glass into an iron mould with spikes that resemble the surface of a pineapple.
You can get this unusual look by putting hot glass into an iron mould with spikes that resemble the surface of a pineapple. This glass has a design all around because of the spikes poking through the surface. All of the glass is then re-molten once it has been allowed to cool down. You can see the first layer clearly through this second layer.