Insoluble Salts Can be Removed the Chemical Way Too!
Soluble insoluble salts,removing salt from water,insoluble chloride salts
Calcareous deposits on pottery are easy to remove manually, most of the
time. The pottery is wetted first. Then, any tool such as a dental tool,
dental burr, scalpel or pneumatic air chisel is used to scrape off the
insoluble salts.
Sometimes, a chemical cleaning might be required, especially if shards
have to be cleaned. Of course, the general process of a thorough pre-wetting
of the pottery (especially the paste) remains the same. If this is not
done, the acid that is used for cleansing gets absorbed into the ceramic
body. There is a choice of three acids that can be used—oxalic acid, nitric
acid, and hydrochloric acid.
The procedure is as follows: wet the pottery item thoroughly, immerse
in acid for around and hour or two (to allow for complete evolution of
gases), rinse under running water, and dry it.
Now, if you have to make a choice between hydrochloric acid and nitric
acid, it is advisable to go in for the former. Since pottery objects come
with glazing, the 10% or 20% hydrochloric acid proves safer. Yes, this
acid can possibly cause the color of lead glazes to fade, resulting in
a milky appearance; but it is still better than nitric acid. Nitric acid
tends to be stronger and even a 10% or a 20% solution can lead to dissolution
of lead glazes. So unless you are an expert in its use, you better stay
away from it.
Oxalic acid is to be used only if iron stains are to be removed. If you
should find any, then after completing the above procedure, rinse the
item under tap water. Now, soak it in a 10% oxalic acid solution for a
few hours. When you feel confident that all the stains have been removed,
take out the piece and give it a thorough rinsing under running tap water.
Finally, dry it completely.
In the case that you feel apprehensive about keeping your ceramics soaked
in acid for such a long time, use a cotton swab soaked in acid. A few
drops can be dropped on different locations on the surface each time.
You may keep wiping off the acid or rinse the object. The process can
be repeated several times. After all, the fear is very real when it is
concerning glazed pottery antiques that can never be replaced! Especially,
earthenware and terra cotta pieces experience deterioration faster when
in contact with acids for lengthy periods of time.
Do you own ceramics that come with a carbonate temper? This would mean
objects with a shell or calcium carbonate. Well, if you wish the tempering
material in the paste to be retained, hydrochloric acid and nitric acid
are both to keep a distance.
On a final note, it is advisable not to play with acids if you are an
amateur in the arena of conservation of pottery. It is far safer to go
in for mechanical cleaning or just hand over the job to an experienced
conservator.
