To make vegetable parchment, plain paper is briefly dipped in sulfuric acid. The acid swells and partly dissolves the cellulose on the surface, which then fuses into a dense, translucent layer. Once rinsed and neutralized, the sheet no longer lets water or grease through. The French still call it 'papier sulfurisé'. The process dates from the 19th century, and many modern baking papers add a silicone coating.
Chlorine on its own is fairly gentle. But when it combines with urine, sweat and other grime from swimmers, it forms chloramines, which cause stinging eyes and that classic 'chlorine smell'. A well-kept pool barely smells at all. Shower before you swim and never pee in the water.
Muscle mass slowly shrinks with age, putting independence at risk. But in 1990, a study had nursing home residents aged 86 to 96 train their legs for eight weeks: their strength more than doubled. Muscle responds to training at any age. Getting up from a chair without using your hands is already an exercise.