I don't actually know when or for how long this lovely range of surface decorated pieces was produced. They mostly seem to be owls, apples or miniature bottles in various shapes - there are a few on ebay just now, easily found under a search for Mdina - but they're not always available. They make quite good money!
I've got an owl and a tiny "squashed flat" flanged bottle.
The silvery, yellowy, goldy lustre-y effects are the result of the glass and silver metal reacting (silver metal ions dissociate from the chloride ions in intense heat - it's the silver chloride salt which is used - but I don't know precisely how this particular effect was achieved.
At the moment these are filed under; "Collect now, find out about later."