Polyvinyl chloride, which is also called PVC, harms photographs. Yet, it is not always clear whether a specific product contains PVC, and labels may be misleading. One indication is that the plasticizer in some PVC products smells like a new car. A better solution is to look for the chlorine that is present in PVC.
Here’s where a bit of chemistry comes into play. This chlorine reacts with copper wire to produce a green flame, so all that is required to identify PVC is an open flame (a gas stove works well) and a piece of copper wire. Wrap the suspect material around the copper wire, heat, and you will now know if the material is PVC. This procedure works because photo-safe plastics do not contain chlorine. See BEILSTEIN TEST: a simple test for Halogens (Chlorides) for more details
If you don’t like this approach, you can always buy a $50,000 XRF spectrophometer.