Amber
In Baltic countries, amber is often treated in autoclave, mainly to produce and enhance the colors and visual effects  thus creating beautiful jewelry. When gradually heated in an oil-bath, amber becomes soft and flexible. Two pieces of amber may be united by smearing the surfaces with linseed oil, heating them, and then pressing them together while hot. Cloudy amber may be made clearer in an oil-bath, as the oil fills the numerous pores to which the turbidity is due. Small fragments, formerly thrown away or used only for varnish, are now used on a large scale in the formation of "ambroid" or "pressed amber". The pieces are carefully heated with exclusion of air and then pressed into one mass by intense hydraulic pressure, the softened amber being forced through holes in a metal plate. As mentioned, the product is extensively used for making cheap jewelry and articles for smoking.