Purification of highly viscous pre-purified glycerol to purities of more than 99.9% was performed by solvent-aided melt layer crystallization. Two different setups were used and suitable assumptions for data evaluation that makes results between the setups comparable are presented. Adding 5-30 wt%. of 1-butanol to the melt drastically increased the separation performance of a layer crystallization. Purities of up to 99.95% were reached at growth rates of 10(-7) mis, even without post treatments. At higher growth rates or without 1-butanol, layers of lower purity can be grown and then subjected to a sweating like post treatment, which is effective but does not compensate the influence of solvent or growth rate. Results suggest an effect of migration of liquid inclusions in the crystal layer. (C) 2016 Elsevier B.V. All rights reserved.