In the fourth continuation of this article the restoration of minimal modern art is discussed, as is the necessity of prior tests on models. Many of these art objects are so sensitive that they would have to be protected entirely from the outside environment. Collages present special problems because of the heterogeneous materials used and the effects of the adhesives holding them together. Dry adhesives are of great help in these cases. Finally, in the happenings the destruction of the art objects becomes part of the art form, the borders of paintings, sculpture and performing arts are breached. This makes conservation in the conventional sense impossible. Understanding of a multi tude of materials and relationships thus becomes a requirement for the con servator. (See also <i>AATA 13-740 and 13-741.) -- AATA