1. Fresco is a mural painting technique-- a wet coating made of sand and lime, applied to the wall, followed by pigment. The resulting murals are often brightly colored and heartbreakingly fragile, quickly ravaged by humidity and heat. Salt is a leading destroyer of fresco-- in the air, carried by ocean breezes, or in the sand mixture applied before the paintings, or else deposited in the very walls that the painting is placed upon. In some cases, crusts of salt would spring up over the painting like a coral, or a mold, bleaching everything in it's path. The Italian masters would wash the offending works with milk, egg wash or talc powder.
2. Leonardo da Vinci used entirely new techniques on his Last Supper, painting with an experimental oil technique (not egg-tempera and water, as with fresco). As a result, the painting was already dangerously close to destruction even during his lifetime. In the 14th century, painters depicting the Last Supper placed Judas alone on the close side of the table, back half-turned to the viewer. When Leonardo painted his famous scene, he placed him among the apostles, shadowed and dark skinned. He leans away from Christ, clutching his bag of silver, spilling the table's salt with his elbow.
3. Artist Sigalit Landeu speaks of the Dead Sea as a collaborator; a recent piece of hers went viral, called "Salt Bride." A black gown is submerged in the water, where cities and channels of salt crystals accumulate and build across it's surface. Photographed underwater, the dress is a white ghost, too heavy to lift back to the surface.
4. Three years ago, my grandfather --newly widowed-- came to Thanksgiving. Having some opinion about my mother's cooking, he snuck salt packets to the table, hidden in the cuffs of his jeans, to be sprinkled over the food when no one was looking. It remains the only time I've seen him attempt subtlety.