A number of treatments have been done to amber for centuries. Amber is not crystalline, like some gems, and it has the ability to soften or melt and reform. This property is called thermoplasticity. While much amber remains natural - aside from shaping and polishing - lower grades are commonly reworked to make larger pieces from smaller ones. But until recently, the final product has remained amber or copal, same as it started; and these processes have always left clues that a carefully trained observer can identify.