Thanks @Ric, (I think—I just went on a torrent--oh well this is just me)
A slag is a single stream marble meaning there was one stream of glass, one white and one transparent coming out of the Kiln/Machine to complete a glob of glass that was transformed into the cute little orb😁 that we all enjoy today.
In the older slags this meant one pot containing two colors—one white, one transparent color. They were both mixed (no double dipping here—lol).
Glasses do not mix color wise—they just get along with each other sometimes. (Many times, it does not get along and that is why we see so many “experimental” types that were dug. Some are very cool to collect but never meant for general sales)
The “Wire Pulls” are a different animal and I truly believe that they had an injection process that revealed the one continuous line that formed the “Wire Pull”, so two tanks in a two-colored marble.
This could not have been achieved in any furnace without the addition of another tank of glass feeding the final marble imho.
The Kiln was the machine, not the rollers or the cut knives. It was stationary and operated with gravity and intense heat.
Generally, the “machine” in the Machine-made world had multiple colors involved—all from the same heat source and this is where it becomes complicated.
I look Forward to @Alan chiming in here, he has a wealth of knowledge.
Marble—On!!