Remelting white gold

Hi to all, I am placing a question that I should have known the
answer already but I always liked a second opinion from you,

The question is about remelting the scrap that remains of white gold
18ct, which I mix myself with the pure gold and one-third alloy of
the quantity, the second and the most the third time. When comes to
milling the re-melted white gold it starts to crack on the edges and
even breaks at times when getting it to a thin gauge on the flat
milling machine. I wonder whether it would have been right if I
would have added a ratio of the pure yellow gold with the scrap. I
have tried this once, but I couldn’t see any difference.

Does anyone of you have found the magic formula how this can be
solved out and the re-melted white gold is good again for
manufacturing (by hand) .