When I made this, I was trying to replicate a cup I bought from a Mexican import store down in Tucson. I’d asked the guy how it was made, and he’d started into a much-rehearsed explanation about how they take glass and get it really hot on the end of a pipie. I was like, yeah, yeah, yeah, but how are the striped lines done? Is this an off axis technique or a color stripe that was dragged? He continued that after you get the glass hot, you blow into it. I said, sure, I know that. and then you make a jack line, shape it more, put it on a punte, break it off, shape it more, but how were the stripes done? After you blow into it, he said, you make a hole, and that makes the cup.
So, a fruitless man-splaning sort of conversation.
I did take a picture of the original cup, and showed it to my glass instructor. He thought it wasn’t an off-axis technique (but he demonstrated how to do that) but that it was just a colored stripe, dragged to make the lines move. We used a tool, and I forget what it’s called, but it’s basically two rollers, offset and clamped to the marver table. When you daub the glass with a molten bit of color and spin it, you get a very even spiral from one end of the glass piece to the other. After that’s melted in, you can use tweezers (ideally, a hooked wire, but that tool wasn’t anywhere to be found) to drag the surface of the glass. It’s a similar technique to what you do when you make end papers using colored inks floating on shaving cream. I’ve also seen people do this technique of dragging swirled lines on the surface of desserts of cups of cappuccino.
The blue in this is more subtle than I expected.