Wednesday, March 10, 2010

ADVICE FROM OUR READERS

Thanks to all the readers who gave advice about the disintegrating art pottery we wrote about in last week's tip. They suggested the cause was mice, hatching insect eggs, termites, pressboard or Chinese drywall fumes, or an old chlorine bleach cleaning. Other suggested causes include a change in humidity or altitude or temperature. Or possibly the pottery froze while being shipped; then when it defrosted, it chipped. And don't ignore the possibility of old repairs. Here are a few of the most interesting suggestions in the blog. We haven't tried any of these, so be careful. For more, go to (Tip, March 3).

Petercdale, in two posts, said:

It sounds like the pottery was washed in a bleach-like liquid. You must cut off the air around that. A first good step must be to spray a clear lacquer glaze in matte and/or gloss over the whole piece inside and outside. This seals the item from air that is probably causing crystals to form through the normally unseen craze lines and under the outer layer of glaze. The crystals form from the digestion of the middle layer of clay. Pottery and similar items are formed in 3 layers--outside glazing, than clay, and then by inner glazing.


This also may have contributed to the problem: The difference in expansion/contraction characteristics which has the inner layer of clay expanding and contracting at a different rate than the inner/outer glaze does. This forms the craze lines you now see. So it could be the combination of craze lines absorbing cleaning liquids that force the outer glaze to crumble. Again, wipe it carefully to knock off any loose stuff, then spray them. The lacquer glaze easily comes off later by dipping in acetone, lacquer thinner or MEK. Lacquer thinner of the three is my choice. Observe the warnings on the chemical cans and lacquer spray glaze can and wear rubber gloves and approved mask. These may all be available in an auto supply store (Pep Boys or Auto Zone or a pro paint store). Good Luck.

John wrote: One of my customers had the same thing happening. She found out that her grandchildren were throwing darts at the wall!!

Anonymous said: Could this be related to the corrosive effects of Chinese-manufactured drywall? See links below.


http://www.cnn.com/2009/US/11/23/chinese.drywall/index.html

http://www.chinesedrywall.com/

3 comments:

CCAntiques said...

As an ex art pottery dealer I can attest to the fact that many people have tried to remove dirty glaze cracks (crazing) by soaking the piece of pottery in chlorine bleach. As the chlorine bleach soaks through the tiny cracks in the glaze it then soaks into the clay and reacts with it. A fine white powder will slowly start to form, seeping out through the crazing. You can wipe or rinse off that powder as much as you want but its usually too late. The powder means a slow reaction has started and minerals are precipitating out of the clay. The piece of pottery will slowly disintegrate. Soaking in distilled water for long period of time may help slow the process but I never found it to help much.

All that being said, if you want to remove the dirt that can settle in crazing soak the pottery in hydrogen peroxide, the kind you can buy at beauty supply stores. I've soaked pottery for several days in a bucket of strong peroxide to remove darkened crazing, with very good results. You need to then soak in distilled water afterward to remove the peroxide. But you wont have a disintegrated piece of pottery if you use this method of cleaning.

Lenore Gusten said...

Hi,
For pots that may have been washed with a bleach based product repeatedly or simply soaked in bleach, we would suggest a simpler, more environmentally friendly approach.

You should soak the piece in a solution of white vinegar and water. The purpose of the vinegar is to neutralize the effects of the bleach and stop the disentigration of the piece. After soaking the piece in the vinegar solution, clean and soak in distilled water to remove the vinegar.

Should you need to lighten the crazing lines on a piece, never use bleach. Instead, use hydrogen peroxide, the kind sold at the beauty stores for bleaching hair. You can soak the piece in the peroxide then wash well and soak in distilled water. (Use gloves) Some pieces may need more soaking than others.

Lenore Gusten
Gusten's Restoration Studio
www.gustens.com

konoponop designs said...

vinegar is still acid....the best thing to do after cleaning any item with bleach or peroxide, or vinegar or any other acid based cleaning product, is neutralize the acid with baking soda!!!!

It works.