The Question of Lead Poisoning and Ceramics

 By:  George Wells 

This question concerning possible lead poisoning associated with the use of antique china is one that surfaces frequently.  (I have answered this question perhaps a dozen times over my years in the FBICC, and I am sure that I am not the only person being asked.) Here is the best answer I can give you:

The pottery (greenware) is not a significant source of lead. In the formulation of pottery of such types as ironstone, none of the components being used (such as flint, Cornish stone, Kaolin and ball clay) contained a significant amount of lead, and contemporary analysis of pottery bodies confirm this observation. Therefore, any crazing associated with the glazes that cover such pottery would not expose a user to any dangerous pottery components. In rather extreme cases, the crazing COULD potentially expose a user to food contaminants or any associated biologics which may have at some point infiltrated the pottery through the compromised glaze, but I have never heard of  a case where a disease vector included crazed dish- ware.

The glazes used on some antique china, including both early and later ironstone body types, did sometimes include significant amounts of lead, usually added to the glaze formulation in the form of “white lead” (lead oxide), the proportion of white lead in the glaze falling in a range of 20-40% by weight.  Before addressing the safety concerns associated with lead glazes, it is important to note that not all glazes used on antique china contained lead – equally lustrous glazes which did not contain lead were sometimes used, just as not all “crystal” glassware is “lead crystal.”  (Note that lead crystal stemware also contains lead in the 20-40% range.)  There is no way to distinguish between lead-containing glazes (or stemware) and non-lead-containing glazes (or stemware) without performing a destructive chemical analysis of the items.

Regarding the safety concerns associated with the use of lead-containing dinner-wares (including both lead-crystal stemware and lead-glazed dishes) the following observations are relevant:

1.    In the cases of both lead-crystal stemware and lead-glazed dishes, the manufacturing processes result in the lead being chemically and physically sequestered in the structure of the item. In the case of the lead-crystal stemware, the lead is “frozen” in the matrix of the glass, and in the case of the glazed pottery, the lead is similarly “frozen” in the matrix of the glaze – which is really just a thin coating of glass covering the porous pottery. In this “sequestered” state, the lead cannot escape (for the purposes of poisoning someone) unless the glass or glaze dissolves to a significant degree. This CAN happen, but only in very unusual situations where the glass or dish has been used to contain a particularly acidic or corrosive substance for a prolonged period of time, after which the corrosive substance is then ingested.

2.    The improper formulation of a glass or glaze could render the finished article more susceptible to hazardous degradation than would usually be the case.  If such degradation has occurred, the surfaces of the glass or glaze will become etched (losing luster). This deterioration of surface integrity is occasionally seen when dishes are cleaned in concentrated hydrogen peroxide for extended periods of time, and is an indication that a bit too much sodium carbonate or other fluxing agent was used in the glaze formulation.  You should discontinue use of any glass or dish that develops an etched appearance.

3.    Lead-containing stemware has been used for centuries to serve wine, a beverage of some measurable acidity, and I don’t believe that any significant health risk is associated with this use. It would seem reasonable to conclude that the normal use of lead-glazed dishes is equally benign.

4.    Some decorative pottery is simply painted (not glazed) with highly toxic enamels, such as cadmium-containing bright reds, oranges and yellows.   Decorative pottery of this type is not in- tended to be used for food and/or beverage consumption and should be labeled with warnings to that effect. If misused, the pottery displaying such warnings will rapidly deteriorate and subsequent poisoning may occur.