Not sure if this is much help. last Sunday at an antiques fair i saw what i thought was a Whitefriars lotus type bowl with flattened sides.
i'm probably way of the mark but this could have been a frigger.
Looking at your posting reminded me of a bowl in the Elfverson catalogue (made by Stromberg) which has the same amount of rings,
similar base and they did a colour called tourmaline green.
The bowl is given as 9 inches diameter, but with flattened sides this might make it similar to the length of yours.
Pure speculation, but it might be a lead.
Tim