After contacting the manufacturer of BCS's holder, I have some information that may shed some light on this question. Yes, BCS holders do contain PVC's, otherwise knows as Poly Vinal Chloride...
The admission by BCS that their product contains polyvinyl chloride (PVC) is consistent with the Beilstein test findings that show the presence of halide-bearing compounds in the graded slabs. So the integrity of the Beilstein test is not in question, it is the interpretation of the results. That is where my observations in comparing the PMG and BCS holders come into play. The BCS holders feel more pliable than the stiffer PMG slabs, and I find that BCS holders scratch and cloud easily from contact. That tells me BCS holders are made of softer material. Whether that means BCs holders are safe for long-term storage or not is unknown. The information provided by BCS is ambiguous, and it's a safe bet that I'm not driving to Kitchener to read a technical report. It's also unlikely that anyone is going to run an experiment where they observe the changes in notes housed in BCS holders over a 20 year period.
