Geo.. all colours , both the enamels and acrylic ones , need to be stirred as long as their tone got the same solid tinge without any dark or light streaks and clumps.. Unfortunately these metalic ones are more prone to getting worse of quality. A such multi-tone of the silver usually means that a paint is losing its properties or there is wrong ratio of the thinner to the paint pigment that causes getting the silver dust worse.. You may try to get some of the paint and transfer it to another container and then add some of a fresh thinner. If the colour can be stirred well it means there is less of the thinner in the paint. But if it gets a darker tone or becomes again the multi-tone the paint is useless.