Roman geometric mosaic. Notice how 'loose' the pattern is. If this was done following etched lines or sinopia then why is it not more precise? We just don't know how much they did by eye.Photo copyright Steve Richards
Bellerophon riding a Bull, Algieria. Notice the 4 motifs, four strand guilloche pattern but it is one strand that turns back on itself as there is an odd number of pattern repeats (you work this out by counting the number of single white tesserae across the top line).
We know it is a four strand guilloche pattern by counting the number of single white centre tesserae on a diagonal line then add 1 to that number. This gives us the number of strands that normally make up that pattern.
An even number of pattern repeats (the number of single white tesserae across the top line) would create two separate strands. Photo copyright Steve Richards