We wanted to make a circular mosaic 1.6 metres in diameter for our garden patio, so we chose a design from the Roman villa at Bignor, Sussex, which would work at that scale.
It has the head of Medusa in the centre and a 'guilloche' twisted rope design as a border - perhaps not the most friendly motif to invite us into the garden!
We could have made the mosaic sitting on the ground, but we preferred to make a round table using large sheets of chipboard fitted onto a Workmate.
The pieces sawn off round the edges will be useful later when the mosaic is cut into sections to be transferred outside.
We obtained coloured marble tesserae and technical advice from the Mosaic Workshop in London.
Now for the master-stroke! We went on holiday for a few days leaving my father (a design engineer) to draw out the strong lines of the design for us on brown paper taped to the worktable. He drew the design in mirror-image because we shall be making the mosaic upside-down.
The guilloche twisted rope design round the border is constructed as you see here, with each segment being 12 degrees.
Here you can see him assessing whether the design has been drawn to the right scale for the size of the tesserae, bearing in mind that a small gap needs to be left between each piece for the grouting.
(We had previously marked the underside of the paper to show the centre of the design and other anchor-points).
If you are interested in adapting our design to make a rectangular mosaic, this drawing shows you how to make different three-strand borders and take them round a corner.
All measurements are in millimetres.
Each of these patterns repeats every 76 mm (to the centres of the circles) and it assumes that you are using tesserae of 10mm with a small space for grouting : 12.5 mm in all.