Pamela - thank you for your generous and kind comments. :oops: I am so glad that you are enjoying them, it makes all the hard work worthwhile. Thank you.
The Derby aka Pinwheel pattern is very interesting. It was made by BOTH Inwald and Sowerby - so don't change your records yet. We have written about the two versions of this pattern in our books and also in the Czech Special (on Inwald and Rindskopf) where we show a close up photo that we feel identifies the difference between the two manufacturers versions of this design.
Inwald made a huge range in this pattern (shown as Piccadilly in the Markhbein catalogues). And to really confuse us all, both makers produced Carnival Glass vases! If the items are in purple or blue Carnival (both are rare, but blue is very rare) then you can bet it is Sowerby.
The one characteristic that I always advise people to use to tell if a piece is Inwald is the highly polished (mirror shiny ground
Again, my thanks Pamela