On large boats, which remain out for two or three weeks at a time, the oysters are left on deck overnight, and the following morning they are opened by means of a curved knife (_miflaket_), four or five inches in length. The smaller boats working near shore convey the catch to the land for the opening and searching for pearls. The Persian Gulf pearls are commonly not so white as those from Ceylon, but they are found of larger size, and it is believed in Asia that they retain their luster for a greater length of time. Many of the Persian Gulf pearls, especially those from _sudaifee_ and _zinni_ shells, have a distinctly yellow color. Tavernier made a curious explanation of this. He stated: As for the pearls tending to yellow, the color is due to the fact that the fishermen sell the oysters in heaps, and the merchants awaiting sometimes up to 14 or 15 days till the shells open of themselves, in order to extract the pearls, some of these oysters lose their water during this time, decay, and become putrid, and the pearls become yellow by contact. This is so true that in all oysters which have retained their water, the pearls are always white. They are allowed to open of themselves, because if they are opened by force, as we open our oysters in the shell, the pearls may be damaged and broken. The oysters of the Manar Strait open of themselves, 5 or 6 days sooner than those of the Gulf of Persia, because the heat is much greater at Manar, which is at the tenth degree of North latitude, while the island of Bahrein is at about the twenty-seventh. And consequently among the pearls which come from Manar there are few yellow ones found.[120] Tavernier was more familiar with the pearls themselves than with the methods of the fishery. The yellow color is not due to contact with the putrefactive flesh, and is independent of the manner of opening. In fact, if putrefaction caused the yellow color, this shade would be far more prevalent in the Manaar or Ceylon pearls than in those from Bahrein, for practically all of the Ceylon oysters are permitted to putrefy, whereas only a portion of those in the Persian Gulf are opened in this manner. Furthermore, notwithstanding that it is nearer the equator, the heat at Manaar during the pearling season is not to be compared with that at Bahrein when the season is at its height, for the Persian Gulf during July and August is notorious as one of the hottest places on the globe.