Thanks for the extra pics Andrew. I have noticed a couple of somethings about the pink enamel used in these which might interest you.
It's clear, but it doesn't seem to always behave like other enamels when it gets hot and melts - it doesn't seem to do it smoothly, but in tiny bits. There are often a lot of tiny, long upright bubbles in it, and there is a general impression of oiliness (but in an attractive way!) about the appearance and texture.
Another really weird thing is that in some pieces, but not others, fluorescent strip lighting will make the pink turn green. There must have been two different kinds of batch of pink, one produced using different metals to the other.
Mdina short attenuated bottles with red/brown spiral swirls like that and are from around the mid-70s and into the '80s, with those vibrated marks. Not overly common in this colourway, but not rare.