The crizzle effect is produced the same way in all things crizzled - it was done before the stones got "invented".
Plunging hot glass into cold water to crack the surface, then introducing something into the cracks and further casing (or not).
It was done by glass manufacturers long before Harris set Mdina up - like most techniques in glass work - it's a very old one.

I couldn't pin anything down to certain years with the information here. Just that they are early and were not the sorts of designs that really got continued much. Around then.