Coffee cup looks foggy after rendering

Hello! I’m following BlenderGuru’s donut tutorial, and right now I am modeling the coffee cup. The problem is that when light passes through the glass material, the cup looks kind of foggy (see attached screenshot). It’s a weird black-spot pattern that’s present on the side of the cup and in the cup’s shadow. When I turn off “cast shadows” in the lighting settings, the problem goes away. This makes me think it’s a problem with how the light is interacting with the glass material and casting a shadow.

I’ve tried a lot of different ideas I’ve found online, but nothing has worked so far. Yes, the liquid is scaled up so that it overlaps the cup slightly. And yes, denoising is turned on.

I really appreciate any help!

They look like denoising artefacts. Try increasing your samples.

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Thank you! I was originally rendering with 256 samples, and increasing it to 500 didn’t seem to make a noticeable difference. But when I bumped it up to 1000, the problem was drastically improved.

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Yep, remember that image resolution is a 2-dimensional thing so you want to increase n*4 unless you use the square sample values option.

If you don’t want to increase your samples then go to render properties and select “Denoising Data” and then render without denoising.

Go to compositor after rendering and
Shif+A > Denoiser.
Attach denoising Albedo, denoising normal and “image” from the “image” node to denoising node and then the denoising node to viewer node

This helps me get far better denoising results than your regular denoising as it uses your intel/amd cpu’s latest denoising Technology compared to blender’s built in default.

Thanks for this - I’ll definitely keep it in mind! :smiley: