If you’ve ever picked up a piece of vintage dishware and noticed a web of fine cracks spreading across the surface, then you’ve seen crazing. These threadlike lines are common on older ceramics (and even some newer ones!), but you may not have given them a second thought. They don’t seem to threaten the integrity of the piece, so why worry?
Crazing isn’t inherently a problem, but as Sam Andrew, ceramicist and director at Seven Limes Pottery, explains, crazing is a breakdown within the surface layer of dishware, the layer that makes it food safe. “A glazed surface, which is essentially a layer of glass, will make your pieces food-safe and watertight,” says Andrew. If crazing is a sign of cracks in that surface, that might mean that the surface is no longer safe for holding food or liquids meant to be consumed.
How seriously should you take that possibility? Here’s what Andrew says.
What Is Crazing?
Crazing is a network of fine lines within the surface glaze of a ceramic piece that can be seen but not felt. It’s caused by a temperature change that leads to the glaze on a piece of dishware contracting more than the piece itself. “All materials expand as they heat up, which is called thermal expansion,” explains Andrew. “Crazing happens when there is a mismatch between the thermal expansion of the glaze and the clay body. Crazing happens to release the tension of this mismatch.”
This can happen in the dishwasher or if the dishes are stored somewhere without climate control. It can also happen after years of moisture exposure, which is why it’s so common to see crazing when you stroll the aisles of an antiques store.
Is It Safe to Use Dishes with Crazing?
“People have been successfully eating off crazed wares for thousands of years,” says Andrew. He notes that studies have shown that simply washing a dish with soap and water will kill bacteria, regardless of whether or not there’s crazing present.
But he notes that there is a caveat here: Whether or not it’s safe to use depends on the vitrification of the clay. “Vitrification is when the ceramic is fired to its top temperature and the silica in the clay melts, filling the ceramic pores. This makes it harder, more durable, and, importantly, nonporous,” says Andrew.
If the ceramic item is porous, then liquid and food items are able to leak through the tiny cracks, and this can allow bacteria to grow over time. “If you imagine milk from a cup of English tea, rotting inside the ceramic surface, that’s what we’re talking about.”
But if the item is not porous, then it should be safe. He suggests leaving water overnight on the crazed surface. If the table beneath is wet the next morning, water is passing through, and it’s probably not food safe.
How Does Crazing Affect the Value of Vintage Dishware?
Generally, minimal to average crazing won’t impact the value of dishware dramatically—unless it’s being sold solely for functional use and not for collecting and displaying.
If an item has extreme crazing, however, and particularly if it alters the actual integrity of the item, then it may impact the value. “Crazing can significantly reduce the strength of a piece,” says Andrew. “The glaze cracks enter the ceramic piece slightly, so it will be easier to break with use.”
Should You Avoid Buying Dishware with Crazing?
If you’re buying dishware solely to use for eating and drinking, then you might want to play it safe and avoid crazing. If you’re buying plates for hanging on your wall or mugs for displaying, then the only thing you need to take into account is whether you like the look.
There is one wild card to contend with, however: You may not be able to tell if there is crazing. But Andrew has a solution. “Sometimes you can’t tell easily whether your piece is crazed or cracked if it has a dark glaze. What you can do is tap it. An uncrazed pot makes a true ringing sound; a crazed or cracked pot makes a dull clunk sound,” says Andrew.
How Should You Care for Dishes with Crazing?
If you do decide to use dishes with crazing, there are a few steps you can take to mitigate any risk. First, only use the dishes for short-term serving and eating. Don’t keep food in crazed dishes for storage beyond a meal. Second, hand-wash these items. The dishwasher is often the culprit in causing crazing to begin with, and continuing to put items in the dishwasher will only make it worse. Lastly, use hydrogen peroxide or baking soda to remove any stains in the crazing, which could be the result of long-gone meals.
