This Crock-Pot brand stoneware / black glazed ceramic liner was positive for lead at 42 parts per million (ppm). [Tested in July of 2014, exact year of manufacture unknown.].
This is a level that is considered safe by all standards (United States and European.) It has also likely been leach-tested. That said I would personally not be comfortable cooking food for hours upon hours in a vessel that is positive for any amount of lead, especially when there are lead-free options out there.
Note: You CANNOT use a LeadCheck swab to test your CrockPot liner for Lead. The Lead levels are far below the detection limits for the swabs. Many bloggers have suggested this in their posts about Crock Pots and this is simply a waste of your money. You can read more about that here.
I do not (and will never) recommend any ceramic lined crock pots because they almost always have lead either in the glaze or the substrate or in both locations. The batch variations (when it comes to the presence of Lead) are too variable and not reliable for me to recommend this type of product (even when one example from a brand appears to be Lead-safe or Lead-free) – especially given the nature of the product and the food cooked within (which includes food often has acidic bases – like tomato sauce or vinegar.)
If you must use a crock pot or slow cooker type appliance I recommend the Instant Pot (link), because it has a stainless steel liner (even though the cooking element is not 100% lead-free, at least the vessel that contains the food is.) The additional benefit of the Instant Pot is that the cooking duration is significantly abbreviated by the nature of the design of the appliance, reducing the potential amount of leaching of Nickel (or Chromium) or other concerns people may have about stainless steel. I do not personally have any concerns for cooking in stainless steel, especially if you rotate your cookware (using undecorated glass, plain [enamel-free] cast iron and stainless steel in rotation and not using any one cookware every day for everything,)
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Please let me know if you have any questions!