Despite the impressive improvements in the quality of large CVD- synthesized graphene sheets over the past years, the highest quality graphene layers are still obtained by mechanical exfoliation of pristine graphitic crystals. However, the method is notoriously tedious and gives a low yield. Worse still, the graphene crystals are relatively small and large layers are often damaged by the exfoliation process itself. We wish to address these limitations and present a novel approach to prepare large graphene flakes with increased yield. To this end we combine the standard mechanical exfoliation with a chemical pretreatment of thegraphite crystals, while preserving the integrity of the graphene layers. ; Fundação para a Ciência e a Tecnologia (FCT)