In Thermogravimetric Analysis, a sample is heated to an elevated temperature, and the resulting change in weight is measured. This can be used to measure oxidations, reductions, dehydrations, and a bunch of other stuff. This is often performed in alumina or steel crucibles, and the sample is compared to an empty reference crucible. Often coupled with Differential Scanning Calorimetry
Typically, crucibles are added to the TGA. A correction is run with two empty crucibles to understand the baseline weight change given a heating profile. Then, the crucible is filled approximately halfway with sample to ensure nothing spills during sample heating. Samples should be heated to a temperature such that they reach equilibrium.
Different peaks can correspond to different things. Dehydration of a salt will appear as weight loss, and oxidation of a transition metal can result as weight gain.