I PEARL ESSENCE 25 



gated. In any event, the ether or amyl acetate must be kept strictly 

 anhydrous. 



If the crystals of guanin are boiled in amyl acetate they lose their 

 crystalline form and become amorphous. This may be caused by 

 loss of water of crystallization, though no mention is made in the 

 literature of combined water and the writer has not gone into this 

 subject. 



Certain other chemical properties of guanin will be referred to in 

 connection with methods of assaying and analysis of pearl essence. 



PROCESSES OF MAKING PEARL ESSENCE 



In the literature many vague references are made to the origin of 

 pearl essence. Many books on pearls, in sections on imitations, 

 mention the use of "ground-up fish scales." As a matter of fact, 

 fish scales themselves do not enter directly in any way into the 

 manufacture of pearl essence. The luster is guanin crystals, which 

 are not found in the scales but are deposited in the epidermis of the 

 fish, parts of which adhere to the scales when they are removed 

 from the fish. It is this epidermis that is the source of the shiny 

 crystals, removal of which from the scales is the first operation in 

 the manufacture of the essence. By far the greater amount of the 

 lustrous substance remains on the fish and is never recovered. The 

 scales are usually collected from the fisheries and washed while still 

 fresh. The first step is to scrub off the lustrous material from the 

 scales. This is done in a lar^e agitator made with a revolving mem- 

 ber, like the old-fashioned ice cream freezer. Domestic washing 

 miachines may be used for smaller scale operations. As little water 

 as possible is used. 



The next step is to separate the lustrous sediment from the wash 

 water. For this purpose large revolving drum centrifugals are used, 

 in which the sediment is thrown against the inside surface of the 

 drum. This sediment is scraped out and is ready for the manu- 

 facturing process. Here procedures begin to differ among themselves. 

 Generally they are directed to making (a) aqueous or (b) nonaque- 

 ous pearl essence. 



AQUEOUS SUSPENSIONS 



The process of making pearl essence of the aqueous kind that has 

 been in use for many years is not very complicated. The scales 

 are obtained in as clean condition as possible and preferably from 

 the belly side of the fish. They are then agitated or scrubbed with 

 water, with or without ammonia, and the epidermis (a very thin 

 membrane) is washed off and becomes suspended in the water. The 

 ammoniated suspension is put through a strainer (not copper or 

 brass) to remove scales and trash. The pearly and protein aceous 

 matter subsides when the liquid is allowed to stand in a cool place, 

 and the supernatant water is then decanted and replaced with 

 fresh ammoniated water. This process is repeated several times, 

 the ammonia gradually dissolving the epidermis and leaving the 

 crystals sufficiently clean for use. Long standing with fairly strong 

 ammonia has a decided purifying effect. 



Pearl essence prepared in this way will keep indefinitely if suffi- 

 cient ammonia is present. It should be kept in bottles having 



