66 The Holy Cross retable The conservation intervention on the wooden support of the “Arma Christi” The annual review of the consolidation effect revealed that the complex situation of the climate, the cutting direction of the boards, and the design of the construction caused stress on the paint layer and subsequent lifting of areas. Thus, the main objective was the treatment of these deformed and endangered painted panels. After completely dismantling these boards, a reinforcing substructure was realized. This involved the installation of four separate rigid frames made of acetylated wood.52 The warped panels are connected to these frames only by the tension force of springs attached to the back of the panels by locally glued wood blocks. The tension of the springs has been set low and can be adjusted if necessary (Fig. 97-100). This system fulfils several purposes: ■ stabilisation of the whole retable structure and of the painted panels ■ additional and reversible support and connection between semicolumns and the body of the retable ■ easy access for inspecting the paint layer and manipulating of the tension springs if necessary Additional long-term effect of this construction can be the retro-deformation of the painted panels. The implemented system with tension springs is an experimental approach and delivers a long-term load situation to the boards without visual disturbance to the retable and with the possibility of regular monitoring. The high relative humidity in the church and the depending high humidity ratio in the wood (calculated 8% up to approx. 30%) and permanent load can achieve plastic deformation of the wood cells both near the saturation of the fibre as well as in dry conditions and can result in a slow retro-deformation. The use of metal springs attached only locally can distribute the load flexibly and without further constructive and invasive operations.53 The applied system is reversible. (Fig. 97 – 100) The four assembled units were adjusted to the retable by a cleat system. Four cleats are screwed to the retable, the opposite members are part of the frame construction. With these cleats, the frame with the attached boards can be hung into the retable without further manipulation (Fig. 98). This system was introduced on both sides, as well to the lintel and to the
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