I am using granular fused quartz to model sandy soils for geotechnical research.  I have recently purchased materials from Mineral Technologies Corp in Cluster SD and from PEMCO in Niagara NY but both products contain trapped air bubbles (picture attached, scale increment 0.5mm) which significantly reduce transparency.  I need a supplier.  US, China, and Japan appear to be the main sources and we would be happy to purchase from any of these locations.