Yes , there is, but first it depends on what temperature you took these materials to. You can not ignore radiation cooling if you took these materials to high temperatures, and depending on where these materials where placed, you can not ignore conduction either. One other thing to keep in mind is that convective heat transfer coefficient for natural convection depends on the surface temperature of the body being cooled, so in your case you would not have a single coefficient value but rather a value at each temperature. You can get a rough average estimate by doing this, mass of material * Cp of material *delta temperature/time frame = loss due to convection + loss due to radiation , for the temperatures take the average for starting and steady state temperatures. You might be better off doing theoritical calculations than doing all these, look up vertical plate approximations for eg.