Alan

German studios (multiple) and factories, mostly around Lauscha. The technique was simple, known and shared.

Late 1800s to early 1900s. Germany.

Divided core.

Vacor with a manufacturing defect.

I'll only comment generally (and not on opal glass). Its junk in the glass. Crud from the cullet pile or just junk in the furnace pot. To no-one in particular: Increasingly, there seems to be a bit of a growing sense, especially among newer collectors that vintage marble glass is (or should be) highly consistent in a marble production process. That the quality should be high. That stray glass colors suggest a "hybrid" or rarer/more sought after type. This mindset doesn't recognize how crude the marble manufacturing process was, how simple the materials, how cost-constrained the production was and how crude the machinery and factory floor were. Vintage marbles were manufactured for between 1/20th and 1/30 of one cent each - all costs in. Silica, gas, machinery, plant, utilities, employees, rail spur, packaging and shipping etc etc etc. It still needed to be shipped to wholesalers, who added their value (order taking, processing, F&C, shipping, salesmen, cost of doing business......). Then they shipped and delivered to retailer parent companies, who broke the shipment down and shipped to retail stores (again, shipping costs). Then the retailer (who had their own store, staff, utilities, insurance costs) sold it for about 1-2 cents each. One of my favorite retailer boxes is an Akro gum box that offered one marble and a stick of gum for 1 cent. One. Cent. With all the production, costs, distribution, shipping - and don't forget making a small profit. The manufacturing process was crude. Materials were added with shovels from an outdoor or indoor pile on the ground. Cullet came from the cheapest sources. Silica isn't a pure pile itself. Pots dissolved in time and needed to be rebuilt - an onerous and slow process. Spinner cups wore down. Funnels got clogged: This is all to say that I see an increasing trend towards expecting current day consistency and quality control in vintage marbles make 100+ years ago with crude processes in crude, dim factories (I have a B&W photo from the Ravenswood factory - wow!) for a tiny fraction of a cent. I encourage everyone to ground yourselves in the reality of 100 years ago where these were throw-away children's toys to be intentionally beat up and lost in the dirt. They had no other purpose. No other future. Consistency and quality of glass wasn't an interest. They had neither the money or time to optimize a child's 1-cent throw-away toy. This perspective can help us all calibrate our expectations grounded in the reality of the past.

Akro, ox.

The top left and bottom left aside - modern MK.

Consistent with modern MKs.

Daylight pics would help with ID. UV doesn't help ID and doesn't indicate age, manufacturer or collectability.

I agree - but there seems no stopping the FB "experts".

Modern MK referred to as a 'dragonfly'.

The modern ones can/do.

Those are modern MK and commonly have some excess colorant in them.

The particulate is cullet pile junk in the glass. Single ingot flopover.

The glass had a little spin on the rollers. If you look for something hoping for it - you will see things through that filter.