Nice pattern on some of those green transitional. Every so often they rival "American quality" speaking of which your group reminds me of most non-american mid-century groups. Similar construction techniques but missing the pop and complex patterns getting cranked out of the US marble factories. Cool group
The marble posted looks To be in pretty decent original shape. A good example for its type and would display well. If any mica Lutz or aventurine, you'd be looking at a premium. The dark streak in the blue looks like contamination or debris but throw a couple sparkles in the mix and interest goes up
Value is so subjective. You probably won't get a straight answer. Some people consider any type of damage = worthless. Other people value the rarity or the color or the pattern etc. Etc etc
maybe it will show up better on a darker background? I'll go along with slag. Could have been a variety of makers unless some sort of defining trait(s). The clear looks like good quality glass
They are better than I could do but they look a bit like they could use some more practice on the symmetry/pattern.
That, plus the more obvious left hand twist, size, and richness of colors all lean towards contemporary practice marbles.
Agreed. Keeping in mind that machine made cats eye marbles have been made for what... close to 100 years now? So it could very well have some age to it. But fairly common in the grand scheme of things.