Reference:Spiral2 Pattern

The spiral2 pattern creates a double spiral that winds around the z-axis similar to spiral1 except that it has two overlapping spirals which twist in opposite directions. The result sometimes looks like a basket weave or perhaps the skin of pineapple. The center of a sunflower also has a similar double spiral pattern. Its syntax is:

pigment {
  spiral2 Number_of_Arms
  [PIGMENT_MODIFIERS...]
  }

The Number_of_Arms value determines how may arms are winding around the z-axis. As a normal pattern, the syntax is

normal {
  spiral2 Number_of_Arms [, Bump_Size]
  [NORMAL_MODIFIERS...]
  }

where the Number_of_Arms value is a required parameter but the float Bump_Size which follows is optional.

Note: The comma is required especially if Bump_Size is negative. The pattern uses the triangle_wave wave type by default but may use any wave type.