When you set the tesserae for a curve in a Roman mosaic be aware of the length of the tesserae you use. The longer the tesserae, i.e. a rectangle shape, the harder it is to turn the curve.
Look at the image,
A shows the rectangle tesserae used and you can see how much more of an angle created for the next tesserae. The greater the angle the more likely it is that you will need to cut a keystone. Any cutting means more work = more time.
B shows where the more 'square' tesserae have been used so the curve can be set without any additional cutting.
C the is a error I see where people assume that using these thinner pieces makes it easier to fill in a curve without creating gaps on the outside. This does work in that respect but it also disrupts the line.
©Lawrence Payne 2012