The processingProcessing of rare earthRare Earth metalsMetal and alloys presents many difficulties due to their extreme reactivity and high temperature behaviors. To properly process these metalsMetal in high temperature liquid form, special attention must be paid to material selection along with operating parameters to allow the metalMetal to maintain high purity specifications. In addition, the long term behavior of these vessel materials must also be considered due to long term creep, corrosion, and grain boundary effects. A case study will be examined here that incorporates all of these technical aspects: a liquid-metalMetal siphon designed specifically for harvesting rare earthsRare Earth after metallization. The principles of materials selection for high throughput rare earthRare Earth liquid metalMetal processingProcessing will be elaborated upon, primarily in areas of high thermal gradient. This material selection in conjunction with operating controls enables new technologies for next generation metalsMetal processingProcessing.