I've got to decide on the base now

I need a base on which to put a background first, then the triskele.
I've got Peltex, which is really firm, but I only bought enough to make the finished square 30".
Oooohhh....another decision made: it will be a square!
I would prefer a circle, but a circle is too difficult to hang well.
If the base is 30", the triskele has to be about 25" across. I've printed the tiled design out 3 times now!!!
But: if I don't use the Peltex, but a normal quilt sandwich, I have no restriction on the size.

The background

The base is the structure, the background is what you see behind the triskele, it is placed on top of the base.
I want it to look as if I had glued music fabrics on it, put white paint over it, then wiped the paint off, exposing the fabric in messy streaks.

 

These are the music fabrics. I am thinking....bleaching....covering with sheer fabrics.....fraying......