From Patek Philippe as an answer to my Query:
Quote-“Regarding the alloy of the white gold we use, we can indicate you that it is composed of 750 °/°°° gold, 130°/°°° of palladium and 120 °/°°° of various metals. We cannot divulge more information about the components. Your timepiece is rhodium plated.”- Unquote
I have no info the palladium content of a Lange in White Gold.
I can confirm that the WG are not plated in any way...neither are the Pt. Platinum cases are the purest metal you can get on a watch case - 95% pure platinum, whereas gold only have 75% gold content for 18k.