Unlike the complete solid solution of silicon-germanium, the temperature-composition phase diagram of neighbouring germanium-tin is characterised by virtually no bulk mutual solubility at ambient pressure. High pressures and temperatures, however, drastically change the electronic and structural characteristics of the liquid and solid states of these elements. This has recently been exploited to remove the ambient constraints leading to a novel tetragonal germanium-tin solid solution near 10GPa. Scanning and field emission gun scanning electron microscopy as well as focused ion beam methods targeting specific regions of analysis of recovered products are employed, documenting here, crystallisation of germanium in a tin matrix below this pressure, reaction of germanium with tin near 10GPa and formation of germanium-tin agglomerates above this pressure. We use these methodologies to prepare new silicon-germanium alloys as well.