CONSERVATION OF ANTIQUITIES — WERNER 595 



aspects of this problem of museum climate and the methods available 

 for the control of the ambient conditions in museums have been 

 described in a recent number of the journal Museum [3]. 



Sometimes this question of the control of environment may arise in 

 a particularly acute form. Such a case is the problem of "sweating" 

 glass — a phenomenon which shows itself in the appearance of droplets 

 of moisture on the surface of glass objects. These droplets were 

 fomid by microanalysis to consist of a very dilute solution of sodium 

 and potassium carbonates, produced by the leaching out of alkali ions 

 by atmospheric moisture. The unsightly droplets can be removed 

 by washing the surface of the glass, but the glass still remains po- 

 tentially unstable and is liable to undergo further deterioration under 

 normal museum conditions. It transpired, in fact, that the only prac- 

 tical method of conservation of such glass objects was to keep them in 

 a dry environment; in practice this meant ensuring that the relative 

 humidity did not exceed 42 percent. This control figure represented 

 the proportion of moisture in the atmosphere when the hygroscopic 

 potassium carbonate just begins to become moist, i.e., when the glass 

 "sweats." The problem was, therefore, solved by constructing special 

 show cases in which the relative humidity was maintained below the 

 critical limit using silica gel as a desiccant [4] . This serves inciden- 

 tally as a good example of how a scientific evaluation of the cause of 

 deterioration is necessary before a rational method of conservation can 

 be worked out. 



NEW MATERIALS IN CONSERVATION 



In the past the materials used in conservation were largely those of 

 natural origin such as glues, beeswax, and natural resins. Con- 

 sequently, many of the techniques evolved as the result of empirical 

 experimentation by restorers were dictated primarily by the proper- 

 ties of whatever naturally occurring material seemed most suitable, 

 and had perforce to be used. Progress was thus constrained within 

 narrow limits. However, advances made in high-polymer chemistry 

 during recent years have resulted in the production of a wide range 

 of synthetic materials. Many of these new materials possess a com- 

 bination of chemical and physical properties which are not to be 

 found in materials of natural origin, and these can be employed in 

 developing more reliable methods for the conservation of antiquities. 



The best way to illustrate the manner in which modem materials 

 can be used in conservation is to select specific examples for con- 

 sideration. These will sen^e to show how the correct choice of a 

 new synthetic material makes it possible to carry out conservation 

 work which would have been very difficult, if not virtually impossible 

 in the past, relying solely on materials of natural origin. 



The first problem relates to the consolidation and repair of an- 

 tiquities which are in a fragile state. In this field synthetic resins 



