What are the main environmental threats to stone?
ÂWater is basically the problem. The conservator at the Cloisters says that 90% of art conservation is controlling the flow of water, and that’s right. Many times you can do a lot by just fixing the roof and the downspouts and that kind of thing. One main mechanism of deterioration is freeze-thaw damage and another is salt crystallization. You can get salt into materials from a variety of directions—sometimes it’s in the groundwater, sometimes you can leach it out of the mortar, and sometimes it forms directly by chemical reaction with air pollution. And once those salt crystals start to grow, they can cause a lot of damage. Are most treatments designed primarily to protect stone from harmful environmental effects or to stop deterioration that’s already started? Are these two very different kinds of processes? They are different kinds of processes, and we may try to do one or the other or both. For instance, if you have an object that’s going to remain outdoors and it’s beginning to de
