Damage from Sodium Sulfate
The main cause of damage to monuments in the Mediterranean Basin is crystallization of salt. One of the most destructive salts in nature is sodium sulfate. (You can get the technical details on our research page.) In this video, you can see the results of a demonstration in which 10 different stones were exposed to this salt for about a month.
Damage from Salt Crystallization
How the test works
The stones are about 5 x 5 x 25 cm. They are suspended with the bottom surface touching a solution of 16 wt% sodium sulfate. Underneath the shelf with the stones are two large tubs containing a saturated solution of calcium chloride, which serve to keep the humidity down to about 39%. A bank of fans along the back of the shelf keeps the air circulating. The whole setup is covered by an inverted aquarium tank to preserve the humidity constant.