Brown stock, the fiber/water solution produced in the Kraft mill, is concentrated in the recovery boiler via evaporation into a substance called black liquor. As the level of concentration increases, raw rosin is created, skimmed off the top, mixed with other chemicals and heated to produce tall oil. The tall oil is stored in tanks and shipped by rail or truck to manufacturers who use it in the production of glue, rubber, ink, soap and lubricants. The remaining black liquor is burned in the boiler to generate steam and energy for the entire facility. Other cooking chemicals are recovered at this stage for re-use in the paper mill.