Model of section of mosaic showing etched guidelines.
Copy of a section of mosaic from Villa Arianna in Italy where some of the tesserae have fallen away leaving the orignal guidelines that were etched onto the base surface (nucleus) by the mosaicsts.
The floor is sectioned up into squares which are then bisected diagonally. A black charcoal wash is used to show a black borderline. The mosaicists have then used whichever elements of the etching they need to create the full geometric pattern.
Wooden batons are used to set the lines of tesserae against. Evidence of the use of these batons has been found.