Apologies for my late reply m and thanks for digging out those links.
Looks like Salviati circa 1900 to me. Who else could make an aventurine rim like that?
Ivo you were spot on.

Bought this plate on ebay and it matches the size and profile of the opalescent plates exactly, even has a heat finished pontil mark and those soft colours are in keeping. I am converted.
Sowerby would have been nice, not this time but maybe one day!