Topographic Models. 265 



oughly dried before being prepared for the cast. The method 

 used by some modelers of placing a frame about the model and 

 pouring in the plaster, filling the frame to the top, is a crude and 

 very wasteful one and not at all to be recommended. In a model 

 of large size — say seven or eight feet square — it would require a 

 derrick to move the mould. It is wholly unnecessary, as, with a 

 small amount of care, a good mould can be made not more than 

 an inch thick, or, at most, an inch and a half. The drying of the 

 mould before use can sometimes be dispensed with, but is always 

 desirable. 



Nearly all American moulders (as distinguished from French 

 and Italian ones) varnish the mould, and thus lose some of the 

 finest detail and sharpness. This is unnecessary. The mould can 

 be easily prepared with a solution of soap so as to leave nothing 

 on the surface but a very thin coating of oil, which is taken up 

 and replaced by the plaster of the cast. Of course, if the model 

 has been sand-papered, no fine work in moulding or casting is 

 necessary, as there is nothing to save. If the subject is a very 

 intricate one, with " undercuts " (as they are called), it is custom- 

 ary to make a waste mould ; as this is very seldom necessary in 

 relief map work, however, the process need not be described. 



To make the cast it is only necessary to repeat the processes 

 used in making the mould. With great care and some skill a 

 cast can be produced but little inferior in point of sharpness and 

 detail to the original model. It is customary to make the cast 

 very thick, and, consequently, very heavy ; this is unnecessary. 

 In our work we seldom make a cast thicker than one inch, and 

 yet are never troubled with changes in the model after it is 

 finished. Even in a very large cast (now in the National Mu- 

 seum), weighing nearly 1,500 pounds and presenting a surface 

 of over 160 square feet, the average thickness is less than one 

 inch, although it required over five barrels of plaster to make it. 

 The cast, after being thoroughly dried, should be finished — all its 

 imperfections being carefully repaired. The surface, however, 

 should be touched as little as possible, as the slight roughness of 

 surface that comes from the original model, through the mould, 

 is removed by any tooling. This roughness adds much to the 

 effect of the model ; in fact, where the scale is large enough, it is 

 sometimes desirable to emphasize it. 



The proper way to paint a model is a matter that must rest 

 principally upon the judgment of the modeler, depending to some 



