Today I cut some 18ct purple gold. When aluminium is added to fine gold,(25% ali,75% gold) under an inert atmosphere it forms an inter metallic compound that is brittle and quite hard. I have made several pieces using it as a supplementary to 18ct yellow and always carving it like I would stone.. This piece was cut for a pendant. It is quit porous and has a chrome-ish look to it. Polished on a Batt Lap with 50K.