Thank you both, that makes sense (although I'm sure spending some time with that old demonstration marble would further improve my understanding if I gave you my address...)
If you've stopped sniggering...
Can anyone explain how butt-cracks are formed?
I know they're common on Jabo, and not uncommon on Champion, Heaton and Cairo, but I've never really understood what causes them.
Thanks Al - (oddly I'd have never have guessed Alley for the second row far right).
Scooby - Champions are nearly always more messy/complex in their swirls
Thanks Steph. There are some of the green stripe and white stripe on black variants in the lot too and they're similar to the red stripe/black widow. I've got some of the modern (well 80's/90's striped ones) and the ones from this lot are similar but not the same - it could be batch variation but the ones from this lot are almost slightly cruder and less 'polished' than the newer ones. My gut feeling is I've picked up a split bag that's probably an early run of the more modern types - probably early 70's (I don't know how well documented the introduction dates of the newer styles is). I'll try and contact the person I bought them from to see if they've got any idea of the date.
Useful id tip - they can be sods to separate from Ravenswoods and Champions (not to mention some Cairo) for those of us who really struggle with swirls. 'Folded up' is how I tend to think of SOME examples, but the 'ear' image makes it even clearer.
I'm certain they're MK - there's a few others in the 100 odd lot that I'm 95% sure is a split tournament bag. I've seen the same ones in photos of other bags. They do look peltish at first glance though - in the hand you can see the glass difference, but it doesn't jump out.
Thank you - that's a lot later than I guessed. The Girl Scout (above) which came with the pink based didn't look like one of the really modern Girl Scout's to me (more early 70's). From the assortment of contents (different sizes) it looked like an emptied tournament bag, rather than of mixed origin.