Sorry to be a bit of a nuisance, but I am not convinced that this is "all sorted".
On the side of it being Monart,
this link goes to a sales site showing a piece of Monart, said to have a coded label. The piece has what I think is the same colours as the OPs item, but in a differing pattern and without the crackle.
But I have a query (which may have been addressed earlier but I don't recall it).
Why, in the OPs item is there an apparent pale blue inner layer with the opal (white) casing the blue? What purpose does the pale blue have? Or is it shadow or something?
The same, but in reverse, so to speak, applies to the item M linked to in the etsy site. That piece has a pale blue edging to the rim as if there is an inner opal layer cased in pale blue ... but the pale blue seems not be showing in the crackled surface - just an opal background.
Sue, could you please ask your brother about this?