Diffraction grating net curtain

 Here is the light reflected from a car through a lace curtain. The cross shape is the result of diffraction by the horizontal and vertical fibres.

The pattern is roughly 1 degree wide. I could see two orders of fringes on either side of the central maximum. Red was the furthest out and violet closest to the centre.

I examined the weave with a magnifying glass and a ruler. There were approximately 4 holes per mm. Using the equation n.lamda = d.sin(theta), then d is approx 0.25mm. For first order fringe, n=1 and theta will be about 0.25 of a degree. That would give a wavelength of about 1000nm to 1 sig fig. That is very close to the range for visible light of 300 - 700nm. Not bad for a ruler and a little finger.