Homebrew PCBs

someone check my math and assumptions, please...

I have 3l of etchant (HCl/H2O2) on its way to a CuCl etchant.

To get the specific gravity from 1.0 to 1.2, that means I need to add
about 600g of copper?  And that solution will etch another 600g of
copper before it hits 1.4 ?  (plus or minus adjustments for increased
volume, added HCl, etc)

(yes, it's at 1.0 now - I weighed 100ml of solution, it's 100g)

Seems like a lot of copper.