What you should find is that the lead inside the partially evacuated chamber appears lighter.
Try it and post the results.
I will. I am curious, how do you expect the effect to scale?
I really don't know, I'd be interested to find out a legitimate test to this.
Ok, so here is my test:
1. Make a vacuum chamber with a window
2. Place a fish scale inside, hooked to the ceiling
3. Check the reading on the scale as an atmospheric reference
4. Pump down the chamber to below 50mTorr, or ~6.58e-5 atmospheres
5. Check the scale reading in vacuum
6. Hook a metal weight on the scale, and take a reading
I will take pictures at each step for record keeping.
Do you have any issues with the test protocol?