How fresco-wrecking salty towers build themselves

CORAL-like formations of salt sometimes sprout up on walls, damaging frescoes and other artwork, and now researchers know why.

Experiments and simulations by Marc Prat at the University of Toulouse in France and colleagues show how salty water evaporating from the pores in these materials leaves behind patches of salt crystals that grow into towers rather than a uniform film.

The towers are themselves porous and suck in more salty water. As they grow, water evaporating from their sides inhibits evaporation from surrounding areas, preventing crystal growth around the towers (Physical Review Letters, DOI: 10.1103/physrevlett.108.054502).

The work suggests that maintaining the right distribution of humidity over delicate frescoes may prevent such structures from forming.

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