Let’s start with the elevator speech:
Get premium white color that provides the look of platinum at the cost of gold. You no longer need to rhodium plate in order to achieve a bright white surface finish. X1 white gold has been enhanced with trace elements that provide grain structure control, ductility, and improved mechanical properties, while maintaining excellent casting characteristics and surface finish. 
Just in case you haven’t heard, X1 is a family of karat white gold casting grain that is formulated to achieve a very good white color without the need for rhodium plating. We sat down with our metals experts to get the scoop on this proprietary metal:
So Shan, what does X1 even mean? X1 stands for extreme white, level 1 color rating. The World Gold Council’s White Gold Task Force’s guidelines for white color specify that level 1 color rated white gold doesn’t need rhodium plating to achieve it’s bright color.
Yea, but can I rhodium plate X1 anyway? Sure you can, just like you can with any other white gold alloy, however, it’s not necessary. An advantage of X1 is that while rhodium inevitably wears off, it’s not needed for X1 so color stays consistent.
Can you tell me more about the characteristics of X1? Sure. We already covered color, but in addition to that, X1 is harder than your traditional white gold alloy. We’ve formulated the metal with trace elements that provide grain structure control, which has improved the metal’s mechanical characteristics like prong bending and ring stretching.
So, if it’s a brighter white color than standard white gold, what solder needs to be used for color matching? Good question. Our metals technology team has developed X1; cadmium-free solders that are color matched to our X1 alloys. However, you can use traditional solders on X1 pieces, but you may leave a visible yellowish-white solder joint or seam.
Sounds good so far, what about casting in X1? Does it differ from casting in white gold? All casting techniques for X1 are the same with the exception of quenching. It’s important to quench within 2 to 4 minutes. Generally speaking, you should quench just prior to the red glow leaving the button. In most cases, X1 may need to be annealed to recover from quenching incorrectly.
On the heels of that question, does X1 have a higher melting temperature? Would I need to use investment for platinum casting in this case? Actually, standard investment for gold casting will provide good results. X1 melting temperatures are pretty comparable to standard nickel white gold alloy temperatures
Recycled metals are a huge topic of discussion right now. Can jewelers reuse X1? Yes, you can reuse X1. We recommend using a 75% fresh mix when remelting X1. White gold alloys are typically not as reusable as yellow ones. If you see any dark inclusions or foreign particles in the X1 scrap, it’s most likely contaminated or depleted and should be submitting for refining.
And what about comparables? How does X1 stack up to Cobb’s Precise White Gold? With regards to Precise White, there are no perceptible differences to the unaided human eye. It’s important to note that X1 white gold is alloyed with a higher gold content to meet all international requirements for gold fineness.
There you have it folks - the skinny on Stuller’s X1 White Gold. See reviews of X1 here, here, and here.