I often get questions in email from folks who have older sets of Rowantrees pottery. A few years ago, most of them centered on the current value (sentimental, quite a lot; monetary, not so much). Others were curious about pottery they had picked up at yard sales or auctions – mostly asking about when a piece was made or by whom (hard to say for certain, but a few minutes of research can provide clues). But two other questions still come up from time to time; durability and food safety.
The short answer to both questions is, “It depends.” I will give the longer answers here and in the order listed above.
The issue of durability generally extends to everyday usage, microwave-ability, and dishwasher safety. How well any pottery will hold up depends on how it is used and how old it is. Nothing lasts forever, and potters do all they can to be sure their products will last as long as possible. I have seen sets of Rowantrees pottery that were decades old and still looked like new. I have also had Rowantrees less than ten years old fall apart in my hands. Rowantrees is earthenware, which is the least durable type of pottery. That doesn’t mean it won’t last a very long time, but you see far fewer pieces of earthenware in museums than you do porcelain (the most durable type of ceramic ware). The big difference is firing temperature and the type of clay used. I can go into more detail on this in another blog post. For now, a simple answer to the question of durability is in order.
Rowantrees was made for everyday use and it would seem most people used it that way. Modern dishwashers and microwave ovens did not exist for some time after Rowantrees was founded, but it did seem to hold up well in both. That said, it tends to heat up in the microwave, so care should be taken when removing dishes after heating (the same goes for Lowell Hill Pottery). Further, food should cover most, if not all, of the bottom surface of the dish to avoid uneven heating, which can cause cracking.
Dishwashers present a challenge for not only handmade pottery, but for all breakable dinnerware. The issue is not the water temperature or the alkaline detergents used, but rather the force of the water jets that can cause dishes to rattle about and bang into each other. Careful stacking can help with this issue, but most dishwashers are built to handle a wide variety of ware thicknesses and to allow sufficient room for water and soap to get in and do their job. More often than not, flats like plates cannot be stacked snugly enough to prevent moving about.
Rattling about in the dishwasher will reduce the life of most pottery. It will still last a good long time, but something thought to last up to fifty years may limp across the finish line after only twenty or thirty. So how long your pottery will last depends on a lot of variables. I doubt it’s the same length of time from one home to another.
Food Safety – an Undefined Term
There is no standard definition for “food safety”, which makes a determination very difficult. In general it is better to look at the toxicity of the materials that went into making the pottery and then determine if those toxins remain stable in the glaze or leach into food. Then the degree of leaching has to be determined to see if the results exceed safe levels.
Don’t get me started on those safe levels. In most cases, they haven’t even been determined. Even when safe levels have been determined, they change frequently as new research shows that we were wrong – again. The best course of action for any potter is to use as few toxic materials as possible in manufacturing their wares.
Just remember, in sufficient quantity, both water and oxygen are toxic.
Rowantrees pottery was made using lead. There, I said it. Most people are aware of this and I get frequent questions asking about its safety. My liability insurance provider would look askance at me making declarative statements of perfect safety, so I won’t do that. There are, again, too many variables. But I will tell you this; to the best of my knowledge, there has never been a case of lead poisoning caused by the use of domestically produced ceramic ware. The incidents involving lead glazed ware causing toxicity involved wares produced in other countries and imported to the USA. And in these cases, the lead leached into food (usually beverages) that was a) acidic (lemonade, tea, orange juice, etc.) and b) stored in the pottery vessels for over twenty-four hours. Since most people put food into their pottery and then consume it in a relatively short period of time, there is no opportunity for lead to leach into the food.
Rowantrees went through a regulatory ringer in 1986 over its use of lead. At that time, the issue was less about food safety than it was workplace safety, but the glazes got tested. Pieces were soaked in acetic acid for twelve to twenty-four hours and then the acid was tested for lead content. While all glazes had passed testing a number of years earlier, the standards had changed and several of the glazes were found to leach excessive amounts of lead. When Rowantrees sought out an independent laboratory to test the glazes, they discovered that this release occurred only on the first time around, and that subsequent tests showed little to no release. The conclusion that Rowantrees drew from this was that the initial high lead levels in the acid were not due to lead leaching from the glaze but from lead fuming that settled on the pottery in the final stages of firing. From that time on, Rowantrees soaked all pottery coming out of the kiln in a vinegar bath for at least twelve hours then washed each item before putting wares on the shelf for sale.
So I don’t consider lead to be an issue with Rowantrees. Lowell Hill Pottery does not use lead due to the aforementioned workplace safety issues and because lead has become such a hot button issue it’s best to stay away from it.
A much bigger concern for food safety is the condition of the pottery itself. Look closely at your pottery. Is it chipped or cracked? Can you see a network of fine crackles on the surface? Has the glaze flaked off anywhere (particularly on the rim)? All of these issues can spell a food safety problem. Pottery that is cracked or crazed (that network of tiny crackles) is inherently weakened. Cracked pots can break when stressed by heat. Try putting hot pasta on a plate with a crack in it. You might get away with it once or twice, but sooner or later you will hear a loud snap and your plate will cleave in two. Chips on the rim leave areas of unglazed clay that will absorb moisture, weakening the pottery. Worse, bald spots on the food contact area can absorb pathogens that will not be destroyed by high water temperatures. Crackles (crazing) can often lead to both moisture absorption and a foothold for pathogens. You can still use the pottery, but I wouldn’t store raw meat on it.
So there it is; a brief (yes, this is brief for me) overview covering issues raised most frequently. I am almost certain that I have left some questions unanswered, so please don’t hesitate to contact me if I have not addressed a concern you have. I will update this blog with any information I can.
UPDATE: Since I published this post I have been made aware of a study done to determine whether or not crazing on pottery surfaces increases the risk of pathogenic illness. The study found that pathogens were easily eradicated on pottery washed in a dishwasher, while dishes washed by hand were somewhat more problematic. Dishwashers typically use water heated to sanitizing temperatures that are far too hot for handwashing. In addition, most dishwashers exchange water between segments of a cycle, while people washing dishes by hand tend not to change water more than once, if at all depending on load size. Most importantly, the results were the same whether or not crazing was present. So it would seem that crazing on pottery surfaces has less to do with potential exposure to pathogens than the manner in which dishes are washed.