Black foil holes

Dear all,
has anyone seen the foil holes that are dark? Like in the attached pictures? What could be the reason of this? Problems with glow discharge? Blotting?


anyone with a similar experience?

What’s the grid material? Is there protein in the holes? Does it look denatured or reasonable/as expected?

thesere quantifoil Au200 mesh R 1.2/1.3. The protein is in the holes and looks as expected, 2D classes with nicely visible secondary structures

Take a tomogram of an entire hole, with small tilt step (1 degree), high defocus (-6 um), then look at things in 3D and let us know what you see.