The author warns against the use of tygon plastic tubing near items of value. The material has been found to be externally-plasticised polyvinyl chloride. Damage has been found on two counts: the plasticiser slowly leaks out out of the plastic onto what ever is adjacent (examples are given of problems with photographic material, paper and item labels); polyvinyl chloride itself breaks down easily with the release of hydrochloric acid. Other plastic materials such as polyethylene, polypropylene, teflon, nylon should be used instead. If the nature of a particular material is unknown, the beilstein flame test should be used to check that it is not PVC.