Reverse Amberina Opal

With opalescent colors, bone ash has been added to the molten glass and the piece reheated when removed from the mold, turning certain parts of the glass milky. In this example, a Fenton Water Lily sauce, the opalescent is quite heavy, running from the outer edge almost to the center. What makes it "reverse?" By definition, amberina is yellow in the center becoming red at the edges. This example is just the opposite.
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