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
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.