ColdBlock’s digestion system historically used quartz or borosilicate digestion test tubes. FWSIR passes through the tube sidewalls to heat the solution inside and rapidly digest the sample. While most samples can be digested by using simple aqua regia acid mixtures, some sample types (in particular, those that contain high levels of silicates) require the use of hydrofluoric acid (HF) for complete digestion. However, the main issue is that HF attacks both quartz and borosilicate glass. So, the standard ColdBlock digestion test tubes could not be used. A better solution was needed – namely, a test tube that could not only stand up to HF but also handle high temperatures and remain transparent to short wave infrared radiation used in ColdBlock digesters.