Choose the grey or Dutch poplar, because its pores are open and its grain regular. The oak and mahogany have veins some of which are hard and some soft, consequently the oil from the pigments gets more deeply absorbed in the soft veins than in the hard ones, and there results a want of smoothness in the painting which increases layer by layer to the end. ,The panel should be rubbed with sand-paper, and for the last rubbing the paper should be soaked in essential oil of petroleum. By this means rays are avoided, the petroleum evaporates and the panel remains smooth without having lost either its grain or its porosity. The panel should be floored and kept in a dry place until it has shrunk -which will be about one inch in a hundred.,Only then should the back of the panel be sized with a flooring composed of equal parts of thick linseed oil and re-touching varnish without siccative, and, when this layer is dry, with another layer of picture varnish. The painting should be done over several layers of white lead, and between each layer the panel should be rubbed with glass paper, and painting varnish with a little siccative should be mixed with the colours. The object of these precautions is to preserve the panel from the attacks of dampness and worms.,,,