If you want to learn how to make this ring watch the video at:

http://www.fluiddesigner.co.uk/ring-emerald-gem-4-leaf-celtic-knot/

N.B. The video shows a slightly different design but the approach is the same.

Clearly any pattern can be added to the ring. Also, with Fluid Designer for 3D Printing there are a wide range available. I use "curves" instead of meshes to create the bracelet. Care does need to be taken with intersecting parts but on 99% of occasions Netfabb Basic will sort out any issues. In this example there were no issues (that is quite rare).