Gaudiesque stitchery

Many thanks to everyone for your good wishes re Gill's heart valve. After a frightening week it is good to have an idea of what might happen over the next few months. 
Although that seems a long time, she might well be fixed for Christmas. 

She was at a Warwickshire Stitchers workshop  in Leamington today, based on Antonio Gaudi's architecture. Her work is in the style of the windows of the Noble Floor in Casa Batllo.   Some tidying up to do and we'll have to sort out how to cut a catenary* shaped mount as it is likely to be framed.

I did try a brief search for making a catenary* mask in Photoshop - but didn't get far.  If anyone knows - please point me in the right direction.
I've made do with an elliptical vignette here.

* Gaudi used the catenary often in his work - it is the shape you see when e.g. a chain is suspended from two posts.
Looks like a parabola but it is not quite the same shape.
I don't think this what our esteemed PM meant when he said we should study more mathematics :-)