Impression (mold) materials are powder mixtures that can turn into liquid when mixed with water. Some of these materials have a more or less complex chemical composition. Others are characterized by mechanical strength and at the same time are easily dissolved in water. In consistency, some impression masses are almost no different from ordinary plaster, but there are those that differ from ordinary gypsum in thickness and are often colored pink; most often, white barium sulfate is used for this purpose, which has the property of emitting a specific odor when it dissolves.
*Gypsum* is an impression material widely used in dentistry. Its harder variety is used for taking impressions. With gypsum you can reproduce all the details of the relief of the alveolar process, clearly mark the border of the gums, and process fine details of the tooth well. Considering the fluidity (ability to expand) of gypsum, gypsum blanks must be rubbed into a spoon.