Lightening

This is the first time ever I tried to made a dress with a pattern that I did myself. I had this shape in mind, and took a paper, even had to calculate angles and get the protractor out (which has been in the loft for 105 years)
The measurements of the skirt went heavenly, but somehow I screwed up the top which ended up enormous. Anyway, cut the long story short, the dress is now fitting perfectly, and is ideal for parties.
To admire: the diamond shaped fabric on the bottom half of the dress.

it's not mine
and it'snot yours.
So whose bum is this?