text: In context of x-rays, opacifiers are additives with high absorption of x-rays; typically these are particles or compounds of lead, barium (often barium sulfate), tungsten, or other high atomic weight elements. Sometimes opacifiers are added to medical implants to make them visible under X-ray imaging. This is especially true in the case of most polymers which are often unrecognizable in the body when viewed using X-rays.