I am currently creating a new race and using the in-game editor I used antimatter as the visual material for their ships, however I can't find an xml file to give me the name to place in this line instead of the Iconian steel.
<Material1>GC3_Ship_Material_IconianSteel</Material1>
Please let me know if I need to give more information, I appreciate any help you can give 
Thanks,
Xenvar