Abstract: To ascertain when individual foundry molds and cores, bonded by a chemical method, have reached the requisition hardness, or still have the requisite hardness, a probe is pushed into the mold or core with a predetermined force, then withdrawn, and after a time interval it is pushed into a fresh point on the mold or core. This is repeated a number of times, each time in a different place, until the penetration is less than a predetermined value, indicating that the requisite hardness has been reached. Apparatus for doing this automatically can be portable and may signal by lamp and/or sound when the hardness has reached the required value. It may be modified to check whether the hardness of a core or mold made some time earlier has fallen below a given minimum value.