Bennington Potters

I'm not a physics person, but intuitively I would think the two biggest heat losses are conduction and evaporative. If both cups are in a similar environment, it would likely be the composition of the conductive barrier and its thickness and the surface area of the liquid that would be the weightiest variables in conduction and evaporation, respectively. Regarding conduction, the thermal conductivity of vitrified china and stoneware is probably not too far apart (although the more vitrified the china--the more glass-like and that would make it a very slightly better conductor of heat), however the thicker barrier will conduct less over time. Stoneware tends to be thicker and I would presume contribute to heat retention in a contained hot liquid. A cup that has a larger liquid to air surface area probably has more evaporative cooling. I'm also thinking that convection plays a role (both in the liquid, but perhaps more in the air) and that could be related to how deep the cup is and how full the cup is filled. I'm guessing, all things being equal, that a cup half-full evaporates slower than a full cup, simply because there is a localized increase in vapor pressure since air convection would likely be decreased.

In the American modern cup, you tend to have a fuller cup since the depth is less than the average cup, so I'm guessing more convection. You have what appears to be a larger surface area from a larger opening, hence more evaporative loss (I've not measured the opening, so I don't know if this is true). You have a fairly thin earthenware cup body, so conduction is likely to be more than a thicker-walled cup. But from the looks of it, the cup holds less fluid than most cups. So the resevoir of heat to be transferred is less.

So I'm guessing the problem with the American Modern cup is multi-factorial. Now I hope a physics person reads this and corrects me where I'm wrong.

Happy holidays!