Whte Clematis - solitary perfection

I have this fascination with a fairly weak plant, which struggles to produce, every year, a few flowers. But what stunning flowers!
Its purity of colour, and the texture reminds me of my mother's damask table cloths.

The flower is about 8 inches (200 mm) across, and it opens on bright sunny mornings, so to find this flower open and smiling at you, down amongst the wilderness of the roses is just pure joy.