Crazing pottery

Glaze Crawling. Glaze crazing or glaze crackle is a network of lines or cracks in the fired crazing pottery surface.

If you are a collector of vintage then you've probably heard of crazing but do you know what it really is? In this post I'll cover the following common questions:. What is crazing? What causes crazing? Are dishes with crazing safe to use?

Crazing pottery

At the Hewitt Pottery we have been developing some glazes using local granites with a high felspatic content. The glazes are beautiful and sparkly but we have experienced some issues with crazing, so during our recent snowstorm, I spent some time reading through books and looking online to see what I could glean. I wanted to share the sum of what I have learned here in three sections: 1 Why is crazing a concern? Crazing can be an attractive feature of a pot and is often called "crackle" when intentionally used, such as on this tea bowl: Intentional crazing, or "white crackle" glaze, on a tea bowl by Richard Brandt. There are reasons why crazing is not ideal for functional pottery, however. Crazed pots may leak if the clay body is not totally vitrified, and potentially be unsanitary as bacteria can grow in the cracks. Structurally, crazing is also an issue as Michael Cardew points out in Pioneer Pottery , p. Vol 40, p. The results after firing showed the comparative strengths of the rods in the proportions 40 : : crazed : unglazed : sound. The results indicate that "vitreous ware with a non-crazing glaze may be three to four times stronger than ware which is crazed. As a potter engaged in producing functional pottery, strength and resistance to thermal shock are important qualities, especially when one considers the competition of industrially produced wares. SiO 2. PbO 1.

The easiest way to detect Crazing is to observe the surface of the material.

Crazing is the effect on pottery which causes it to have a web of tiny cracks over its surface. These are not cracks in the actual structure of the pottery but actually an effect on the glazed part of the pottery. Although crazing is generally a surface affliction, it can weaken the integrity of your piece in time, as it is opening up the glazed piece of your pottery and thus weakening its overall structure. Crazed pots are also not suitable for foodstuffs as they may leak if the clay body is exposed, and potentially harbor bacteria in the cracks. For more information on this, check out our article on how to make food safe pottery. Crazing generally occurs with age but there are other factors which cause immediate crazing which include:. Crazing can also occur when the glaze shrinks more than the body of the ware.

As an affiliate, we may earn a commission from qualifying purchases. We get commissions for purchases made through links on this website from Amazon and other third parties. Crazing in pottery glaze is a network of very fine cracks that cover the glaze on a piece of ceramics. Sometimes potters deliberately want to create a crazing effect, and this is known as crackle glaze. But a lot of the time crazing is considered to be an unwanted glaze defect. Crazing happens when a glaze is too tight for a piece of pottery. Clay and glaze expand and contract as the kiln heats and then cools. This is thermal expansion. If the glaze has a higher rate of thermal expansion, it contracts more than the clay as the kiln cools.

Crazing pottery

If you are a collector of vintage then you've probably heard of crazing but do you know what it really is? In this post I'll cover the following common questions:. What is crazing? What causes crazing? Are dishes with crazing safe to use? Can I remove crazing? Does crazing affect the value?

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Either the body expanding or the glaze shrinking can cause fine hairline cracking crazing to occur. Kiln Tips Toggle child menu Expand. Do you want that kind of low temperature thermal expansion behavior in vessels made from your porcelain or stoneware clay body? In addition to the above, thinning down the glaze may also help reduce or eliminate crazing. It is larger so that may account for that. While potters can be very creative and inventive, they can definitely learn something from industry when it comes to dealing with crazing. Plus sides, it was cheaper than other sites and the customer service here was amazing. Can Crazing Lead to Leaching of Chemicals? Cardew, Michael. I'm still learning and have fired up about 3 times now and all went well Have used this unit 7 times to date.

To fix crazing in pottery, apply a layer of clear gloss glaze over the affected areas and fire it in a kiln at the appropriate temperature. Crazing in pottery occurs when the glaze and clay bodies contract at different rates, causing small cracks on the surface. Crazing not only affects the aesthetics of the pottery but also compromises its structural integrity.

However, adding a flux will often make the glaze more runny. These little cracks can become a favorite hangout spot for bacteria, triggering possible health concerns. The feldspar does contain the offending high expansion oxides of K 2 O and Na 2 O , but if you remove these the glaze is not going to melt enough unless of course it was over melted before. Viewing crazing as a material level problem might be OK for certain highly fritted low temperature glazes, but it does not work for stoneware glazes. Article Talk. In this post, an excerpt from her book Special Effect Glazes , Linda Bloomfield tells you all you need to know to increase or reduce crazing in a glaze! Firing to the proper cone number is critical to help eliminate crazing problems. You can open all the peepholes to let the heat out, but only the top one is typically recommended. Are dishes with crazing safe to use? It is simpler to increase a material already in the glaze than to add a new one. Read on to learn why the the crazing looks brown. If you are a collector and you want to insure your collection, then a pr ofessional appraiser will most likely take crazing into account when giving you an insurance value. Skip to content. Changing the formulation of the glaze may be an easier and less expensive option. In addition, highly melted reactive glazes typically depend on low silica for their unique character.