Tips for Adjusting Jewelry Weight Without Changing Shape or Thickness

Hey there, awesome jewelry designers!
I’m a 3D jewelry design student and I was wondering if you guys could give me some tips on how to make my designs heavier or lighter without messing with the shape or thickness. Is that even possible? If any of you have some tricks up your sleeves or know of any tutorials, I’d be super grateful if you could share them with me!