Different types of base molds may be used to provide a "frame" for arrangement of the specimen and to hold the molten paraffin while it hardens. The most common type is the metal base mold, but other types (eg, plastic disposable molds) may be used. The outer dimensions of base molds are standardized to fit within the sizes of most manufacturers' microtome block holders. The block face (indicated by the arrows) is the centrally located, more deeply recessed surface where the tissue specimen will be placed and arranged. This recessed area, which becomes the block face, can be different sizes (shown in the image) to accept differently sized specimens. The base mold size selected should be based on the specimen type and size with consideration of the microtomy protocol that is expected to be performed for that specimen type.
Various sizes of metal base molds.