Comment by tadfisher
18 hours ago
Only because humidity is measured relative to the vapor pressure at a given temperature. It only matters for preservation when humidity reaches 100%.
18 hours ago
Only because humidity is measured relative to the vapor pressure at a given temperature. It only matters for preservation when humidity reaches 100%.
Is this true? Paper (and I assume papyrus) expands and contracts with varying humidity even below the saturation point, and this motion embrittles and cracks it, no? So consistent humidity is key, and "consistently dry" is much more achievable than "consistently at an arbitrary other point."
Your intuition is more correct: it is not true. The relative humidity of the air matters below 100% as well. I think the parent commenter mistakenly assumed that only "condensation" matters, but materials will absorb moisture from the air even if the water doesn't condense. Entropy drives the dispersion of moisture, and some materials are "hygroscopic", meaning they don't merely reach equilibrium with the air, but actually concentrate moisture from the air and get significantly more wet than the air which feeds it water.