Despite not being exactly sure about colours, the flame pontil mark does indicate a time period between '73 and around '79.
It's certainly not any known range, so most likely an experimental piece. The close similarities it bears with features found in Mdina would, to me, suggest early experimental rather than later. I'd put it near '73.
A rather lovely and interesting thing, but I'd like to see unflashed pics too, pretty, please?