Hi - don't know which uv torch you have, but flagging batteries can make a difference to the strength of visible uranium glow, and it's true that some pieces set the curtains on fire more than others.
From memory I believe the Depression pieces don't have the strength of glow that, for example, some of the earlier C19 uranium glass has - some of which will show their uranium content in bright early morning sunshine - without the need for a torch.
Examples such as this can be seen from a considerable distance at boot fairs and such like (provided the sun is shining

)
If you're keen on collecting u. glass, then you should invest in a good quality torch - £10 should buy a reasonable piece of kit - nothing worse than getting to the boot sale and finding your batteries are low or the torch isn't man enough.
When it's manganese (and not uranium) the colour produced by the uv torch is a subdued, dull, almost greyish green.
You'd be welcome to borrow my two Barrie Skelcher volumes on uranium glass - well worth reading - but I suspect you're either in the Outer Hebrides or somewhere on the Isles of Scilly, and nowhere near London.

You can of course buy these volumes from Abe Books, or similar, and if you're keen on this type of glass they're essential.
Best of luck.
