The author describes a controlled environment made for the protection of a panel painting on loan from Berlin to the Brooklyn Museum during the winter of 1963. This environment consisted of a large sealed wooden case with a double glass door, pans containing a saturated solution of magnesium nitrate hexahydrate (Mg(NO₃)₂ ^. 6H₂O), and a small fan. By this means the relative humidity inside the case was held between 50% and 52%, while that outside varied from 12% to 28%.