The first stage is border molding, which utilizes compound stick or
putty to achieve border impression. The second stage utilizes wash material
to achieve detailed impression, which utilizes polyvinyl siloxane , zinc oxide eugenol. or polysulfide . It's probably washing material that 's ingested. Each individual practitioner may have his own preferred impression material or technique. Perhaps, asking your dentist is the best way to get information you wish to know.