My drawing of the vase is far along enough now that I can calculate the exact ellipses of the designs as well as the shape of the vase. See How to Draw an Ellipse for complete instructions on the ‘pin-and-string-method’ of ellipse construction. Below you can see tracings taped to my drawing of several of the ellipses that I constructed. These were transferred to the drawing by flipping the paper over and tracing over the lines to transfer.
It’s important not just to get the shape of the ellipse correct and symmetrical, but also to make sure that the angle of the ellipse is correct. The closer it gets to eye level, the more shallow the ellipse appears. As it goes below eye level, it looks increasingly closer to a circle. I check these angles with a string and a protractor. The string is tied to a stand at my eye level and I then carry it over to the appropriate circle in my set-up. I measure the angle from the horizontal with a protractor. I use this number to construct the ellipse.
You can see that I’ve drawn the ellipses not just to the edge of the form, but a little further, around the curve, This helps ensure that you don’t draw the ellipse as coming to a point at the edge- a common mistake. If you get this detail correct, your ellipses will look very convincing!