Fady, and everyone else. i have been casting white gold for
years without these problems. i found an alloy that seems to be
near perfect. i use it for 14 and 18kt it does not come out
brittle ever! and i even have taken the same button and used it
to make sheet stock as well as wire stock. i have even melted it
three or four times for different sizes or because of poor ingot
pours. prongs can even be open and closed a couple of times
without breaking. i even use it for pave’. sounds too good to be
true i know, but everyone i give a sample to says that it is all
i say it is. i get this alloy from Heraeus PMR Inc. at 11135
Walden Ave., Alden, NY 14004 (716) 685-2200. the alloy is #40
white.hope this helps you all as much as it did me. oh yes.
usually cast at about 1100 to 1150 depending on the weight of the
piece. melt the alloy and pure gold together in the
crucible,stirring constantly untill all alloy is melted and
mixed. i also Always! use Rey vacu-liners regardless if i am
casting vacuum or centrifical. this really helps releive gas
pressure.hope this helps 
Frank