PRESERVATION OF SPECIMENS IN PLASTICS 13 



he fluid-type designations will help in interpreting the results. While 



orkable results can usually be obtained at room temperature within 

 to 30 hours, more exact indications are obtained if the jars are kept 



frigerated for 4 or 5 days. On the other hand, a much quicker but 



Considerably less reliable indication of the action of the fluids can be 



btained in 20 to 30 minutes by raising the temperature of the jars to 



•etween 70° and 80° C. (approximately 170° F.). The pigment re- 



ponses under such conditions, however, often do not correspond in all 



spects with those obtained at room temperature or under refrigeration 

 nd may consequently give misleading indications unless due allowance 



made for possible variations. 



The types of fluids ordinarily needed for making these tests are listed 



below. Where the indications obtained with these standard fluids are 



ot entirely satisfactory, other intermediate types should be tried in 



rder to obtain closer correspondence with the pH requirements and 



ther characteristics of exceptional specimen material. 



The standard test fluids commonly emploved are: Sorbitol borate 

 ;ypes SB-1035-A, SB-1045-A, SB-1055-A, SB-1065-A, SB-1075-A, 

 5B-1155-A, SB-1165-A, SB-1180 and SB-1180-A; and sorbitol citrate 

 wpes SCX-2035-A, SCX-2045-A, SCX-2055-A, SCX-2065-A, SCX- 

 2075-A, SCX-2155-A, SCX-2165-A and SCX-2175-A. 



Extra specimen material similar to that which is to be preserved 

 should be used in making tests for selecting the preserving fluid, and 

 the parts to be tested should be cut into as many pieces as will be neces- 

 sary to provide at least one piece for each jar to be used in the test. In 

 putting the pieces into the jars it is important to make sure that each 

 piece is completely wetted by the fluid and that it is kept submerged 

 well below the surface during the entire period of the test. 



After the test pieces have been immersed long enough to make sure 

 that no further changes in appearance will occur, they should be re- 

 moved and, after most of the fluid adhering to them has been allowed to 

 drain back into the jars, they should be laid out on sheets of thin cellu- 

 lose acetate film (0.0015 or 0.002 inch thick) and covered with similar 

 film. The excess fluid should then be forced away from the pieces by 

 lightly applied finger pressure, and their appearance then compared 

 I with that of the fresh material. Unless time is taken to dehydrate 

 I these test pieces, however, allowance should be made for possible further 

 change in appearance that might occur upon drying. After a reasonable 

 amount of experience the action of the preserving fluids can in many 

 cases be judged with workable accuracy while the test pieces are still 

 immersed in the jars. 



Since the results obtained with these tests, especially when they are 

 carried out at or below room temperature, are generally similar to those 

 that may be expected when the entire specimen is subjected to preserva- 

 tion treatment, the type of fluid that produces results most nearly in 

 accord with those that are desired should be selected for treating the 

 specimen. When selection of the preserving fluid is made in this way 

 it is not actually necessary to give consideration to the types of pigments 

 present in the specimen, but it will nevertheless be found desirable to 

 note them for the purpose of accumulating information that will be 

 useful in preserving similar material in the future. 



