IR-spectroscopy was used to study the samples of fresh soluble, naturally-aged soluble (a flow of glue taken from a wooden sculpture of 1483) and insoluble (the same flow of glue) gelatin before and after heating the samples to +210°C. The IR-spectra of the unheated samples were typical spectra of collagen or gelatin, with certain distinctions observed within the 1, 4601, 380 cm^-1 region. After heating, the Amide II band shifted to the range 1530 cm^-1 in the soluble gelatin spectrum, the band at about 1,400 cm^-1 disappeared in the fresh soluble gelatin spectrum, and its intensity decreased in the aged soluble gelatin spectrum. The IR spectra of insoluble gelatin before and after heating did not differ in the 1, 560-1,380 cm^-1 region. The changes observed in IR spectra are discussed in connection with the probable structural alterations during the natural aging of gelatins, including the formation of interchain bonds and removal of water molecules.