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Get Rid of Those Soluble Salts from Your Antique Pottery!

Care and repair,removing pottery,monitoring the removal of soluble salts

Despite being in a marine environment, pottery manages to survive quite well. A very basic treatment might be required after recovery from the seas or shipwrecks, to remove soluble salts (chlorides, phosphates, and nitrates). In fact, ceramics can become quite saturated with these salts, or even have the entire surface crusted with insoluble salts such as calcium sulfate and calcium carbonate.

Why are soluble salts considered to be more dangerous than insoluble salts, where pottery is concerned? These salts are hygroscopic (absorb moisture from air) in nature. Since relative humidity tends to fluctuate, the salts can undergo repeated dissolution and crystallization. By the time the salts reach the surface, so much of internal stress has been caused that the object is bound to break. Sometimes, needle-like crystals are also visible; and they can be in large numbers.

Now, stoneware and porcelain are fired at very high temperatures. So, water with its soluble salts may not really penetrate into the body. However, glazed items can end up having salt deposits between the glaze and the body. And as you are well aware, most people do own glazed pottery. If these salts are not got rid of, the glaze will disappear. In this case, you can get hold of an experienced conservator to conduct the necessary repairs. Though a complete washing with a mild detergent should suffice, it is better not to attempt the job yourself. A soft brush is used to gently scrub the surfaces and the edges. Extreme care has to be taken not to mar the surface or remove certain traces on the exteriors and the interiors. These traces could relate to paint, soot, pigments, or food. For consolidation of flaked surfaces or friable surfaces or fugitive paints, resin is used.

The general method for getting rid of these soluble salts is by repeated rinsing. The professional way to do it is to set up a series of vats. While water keeps running into one vat, it cascades into the remaining ones. The water to be used is de-ionized. This results in minimal wastage of water.

Some people put the shards into a mesh bag and place it in the reservoir of a toilet. Of course, the water is changed each day. Because of the continual soaking, the salt contents in the pottery item and the supply water equalize soon. Now, the bag is removed. Further rinsing is carried out in de-ionized water. After several repetitions, the salt levels really decrease a lot. Oh yes, you can monitor the whole process of rinsing with a conductivity meter. It lets you become aware of the fragility of certain objects. So, for extra delicate shards, strengthen the surface with Acryloid B-72 before rinsing.


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