Like many conservators who have undertaken conservation treatments on gilded objects in recent years, we have used a gesso containing barium sulfate (BaSO4) to fill areas of loss. The barium sulfate gesso was employed to allow detection of fill material by x-radiography, because of its higher x-ray absorbance when compared with the traditional calcium carbonate (CaCO3) and calcium sulfate (CaSO4) gessoes that are found on cultural objects. In 1997 Arlen Heginbotham, a summer intern at the Philadelphia Museum of Art (PMA), used x-radiography to examine a gilded American girandole frame that had been treated previously at the PMA with a calcium sulfate gesso containing 10% BaSO4. The resulting x-radiograph showed that it was not possible to discern the BaSO4 containing fills from the original CaCO3 gesso of the girandole. Further x-radiographic examination of fills made with BaSO4 concentrations as high as 20% gave similar results. Moreover, the addition of larger quantities of barium sulfate to gesso adversely affected its working properties: the barium sulfate tended to clump or settle to the bottom of the container and the gesso became gritty. This tip outlines preliminary testing undertaken to identify a non-toxic gesso fill material with a high x-ray absorbance that allows discrimination by x-radiography while retaining desirable working properties.