There's was a patent submitted in 1928 which talks about transparent base glass and it talks about controlling the ribbons somewhat. Mentions "one or more" openings through which ribbon glass could go. I don't know whether this patent was for slags or for more multi-color marbles or whether it was even ever used. It's one which has been mentioned before in possible connection with feathering because it talks about jiggling the glass somehow.
As curious as I am about it I'm reluctant to talk about it 'coz it's a patent - for a machine *shudder* - and it could be years and years before I understand it, at least without some help.
So, my general question right now, which I hope is connected enough to Ann's question, is/was something like Are those patents worth studying for figuring out feathering. Or have the people who know Pelt stuff well gone through them and ruled them out for feathering? Maybe ruled them in for other types of mibs?
And Mike of course knows the Pelt stuff.