the oils from the nuts are still on and around these shells :wink: :D:D:D

I've never heard of this. Learn something new all the time.

My quilt group invested in some to share & made pincushions.
We now regret it because our pins & needles got dull.

I use sand (washed of course, not from someone's sandbox because you would not believe what you will find in that stuff) for pin cushions. It gives a good weight. I do suggest that you make your cushion with a double layer of fabric to ensure the sand stays put.