Care and Repair

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Crazing - Two Views
(both valid - saying much the same thing, but from different points of view)

 

First Point of View

Crazing is minute cracks in the glaze caused by the uneven expansion or contraction of the glaze and the body. Crazing most often occurs in the firing stage of production, but can occur or be expanded by heat and humidity in use or storage.

Two things to remember about crazing:

1. Crazing is Damage -- It is cracks in the glaze. It is a place where staining may occur and it can effect the functionality of the piece. While some crazing may be acceptable (Rookwood sold crazed pieces as 1st quality) to a buyer because of the rarity of the piece or the prevalence of crazing in pieces by that specific potter, a seller should always reference crazing; and

2. Crazing is Not an Indicator of Age -- crazing most often occurs at the time of firing, so the piece has been crazed from birth. Older pieces are more likely to be crazed because of the imprecision of kiln temperatures and less understanding of the chemical reactions between glazes and bodies. And a piece may become crazed after manufacture from use especially washing or drying in very hot temperatures. Also dirt may build up in crazing over time making the damage more apparent. However some new pieces are intentionally crazed as part of the design or in an attempt to make the piece look old. [Peter]

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Second Point of View

Crazing occurs when there is sufficient difference in the expansion rates between the body (clay) of a piece and its glaze. Crazing occurs during the heating and cooling of the kiln. Crazing is not the result of age.

During the time when much Rookwood was produced, the kiln and ceramic technologies were not advanced enough to control or predict crazing. It was only in the middle 1920's that the technologies advanced to a point where most pieces did not craze. Before that time, most pieces (about 80%) did craze, including glossy, semi-glossy (Vellum), as well as mat glazed pieces.

Although crazing was normally not the desired result, at the time, it was not considered a defect. Rookwood sold crazed pieces as first quality and did not differentiate between crazed and uncrazed pieces.

In the current market an uncrazed piece typically has more market appeal than an otherwise equal crazed piece. Auction catalogs typically mention when a piece is uncrazed and rarely mention when a piece is crazed. Buyers should assume a piece is crazed unless otherwise noted. Know that some of the highest priced and most beautiful Rookwood pieces ever produced are crazed. [Frank]

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Cleaning Crazed Pottery with Stains

First and foremost - NEVER - NEVER - use Chlorine Bleach on Pottery. It will "rot" the pottery from within, thus causing permanent, unrepairable damage and weaken the piece.

The following formula will work and WILL NOT damage the pottery -IF you follow these instructions carefully.

Peroxide.... You'll need to go over to your local beauty supply store and ask them for 30% or 40% developer (the 30% is favored over the stronger one as the 40% could enlarge hidden cracks. And it doesn't do a better job, but either will do the trick).

1) For crazing that is only on the inside of a piece, fill up the cavity with the solution or if the crazing is on the outside and there's no cold paint or gold, then immerse the piece in a larger container.

2) Cover the object or container and put it in a safe, warm place for a couple of days.

3) Dump out the peroxide (preferably back into its own container - I use a plastic container with a sealable lid, put the items in then remove and cover the container - to reuse once or twice again).

4) If the crazing is still visible, place the piece into a WARM oven (lowest setting possible) for about 1 hour.

5) After one hour, turn the oven off and let the piece cool down inside the oven!.
NOTE: if you take the piece out immediately you run the risk of having it crack.

Do Not use this treatment on cold paint or gold trim! [Peter]

 

Additional "articles" will be added as we receive them. So keep checking............