Probably not adding anything as I know so little about Ysart/Monart but I just wanted to say I can see exactly what Nigel means.
To my eye, as well as the colour looking quite opaque as Nigel mentions, the way the colour is laid on in the Non-Ysart bowl Gary showed appears to be completely different to the effect of the colours in Orange's vase. The bowl looks to have specific blobs of colour that are not cloudy, fluffy or smudgy round the edges. To me it's as if the colour in the vase has been laid on using powders but the colour in the bowl has been laid on by picking up little hard pieces of glass.
That fluffy cloudy effect is similar to what I see in my French 20's glass, never in little blobs

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