PRESERVATION OF SPECIMENS IN PLASTICS 



25 



pieces of cellulose acetate film (rigid type, 0.002 inch thick) are used as 

 temporary overlay sheets during the cementing operation. These 

 films should be large enough to extend 2 inches beyond the edges of the 

 mounting sheets and thus provide space into which the cementing resin 

 can be extruded. One overlay sheet should be applied to the under 

 surface of the lower Vinylite mounting sheet, and the other to the upper 

 surface of the top mounting sheet. These overlay sheets are tem- 

 porarily attached by spreading on them a thin coating of the water- 



Figure 7. — A heated mounting table can be arranged by placing an inverted metal 

 tray on the lower part of a rectangular or oval roasting pan filled with warm water 

 and supported by another metal tray over a suitable electric hot plate. 



soluble lubricant consisting of equal parts of Span 20 and Tween 20. A 

 flat brush or stiff card may be used for applying this lubricant. 



Processing the Mount 



Applying cementing resin. — The lower mounting sheet, which carries 

 the specimen, is laid on a heated mounting table (fig. 7) which is main- 

 tained at a temperature of between 90° and 95° C. (194° and 203° F.). 

 The cementing resin, heated to approximately 110° C. (230° F.) in an 

 air bath should be applied on the face of the mount in sufficient quantity 

 to cover it liberally, the greater amount of the resin being applied over 

 the specimen and smaller quantities near the corners of the mounting 

 sheet , 



