@Oddball I don't see what you see in the second and third photos, and I'm not sure of your interpretation of the photos from UFiP rotocasting. I only really see the marks in the first photo of the blanks. I don't know if they go all the way through the cymbal, although you seems to be sure. I've seen no evidence of what the structure might be like if you lathed away deeply. I've looked at photo micrographs of Italian cymbals at various scales and I haven't seen anything which might correspond to this "spotting", but I might pass on a link to the guy who does my metallurgical analysis and see what he has to say about the science. I rely on him because metallurgy isn't my area of expertise. You might be correct, but I'd still put the answer as "not yet known". Can you please annotate the third photo with what you mean so I have a better chance of understanding exactly what you are looking at when you say "The third one if you look close you can see the swirls on the finished product."@Chromeo Note that the point I was making earlier (my post of the Paiste 602 bell which Jeff linked to) is that rotocasting marks might go straight out radially, but the artifacts of lathing might go out with more of a spiral to them. I'm unsure, and I'm wondering how often we don't keep things clear because of inadequate terminology. I'm still not happy with our level of understanding. And I would caution you to go back to a previous thread you startedhttp://www.vintagedrumforum.com/showthread.php?t=44958and read carefully what I said about the dates for rotocasting and what we believe a pre rotocast cymbal looks. I just think it is important to attach to right level of uncertainty to our statements which otherwise sound well researched.
Well, in the second pic on the far right row of cymbals you can see black spots on the bell and a few smaller one`s on the plane. My buddy who worked a foundry for most of his life says to me that I can think of them like sun spots on the sun. He explained that after the pour, they spin it while it`s cooling to give the metal a "grain" if you will call it. If you don`t spin it the cast will cool and have an orange peel type of look to it. The spots are different cooling rates and interrupt the grain.
If you run your hand across the black marks in the first pic, it`ll be smooth, you wont feel ripples because the metal inside the mold has no where to go and it packs together and gives it those swirl looks. He`s Brazilian and hard to understand a lot but explains things pretty well by comparing. If you take a ceramic drum stick and stir a spot on the hot cast, when it cools, all the cymbal will look the same except where you stirred it. you will see that "break" in the "grain" like a knot in wood. These casts are thin and easy to make spots or ripple all they way through.
If the mold changes speed while the metal is still liquid, you`ll notice those changes too. If it shakes while spinning, you`ll see changes over one`s that don`t too.
On the third pic I make the pic larger and look close at the bell and mid plane and I can see the ripples but the light is blocking a good look but you can see them on samples here all the time.
I read that story from UFIP but saved the pics. and not the story.
I`ve used a lathe a lot in my life and understand how that process works and can tell you with certainty that they don`t do the record needle thing with the tool. It`ll spin and be tooled, then the tool, product or both get adjusted to go around again, then step on the pedal and move the tool and go around again and at any time you can change out the tool for different lathe marks or knurls or whatever you are doing. If you do the record needle thing you'll get just that effect on the cymbal. The huge size and weight of the tool only to use the itty bitty tip is to control better the force applied (it`s own weight) or make fine adjustments in the cut. A little tool will fly out your hand a lot. A lot of cymbals I see used several different tools to go over previous cuts and get different results in the lathing.
This is not my field of work but it`s easy to understand if you use comparisons instead of terminology. Most marks are made where the air holes are or where the molds come together.
This is not my field so I`m trying to explain as best I can.