Crystallisation is the name given to the conversion of a floating charge into a fixed charge. While much has been written on how charges are classified as fixed or floating and on the theoretical nature of the floating charge, crystallisation is, by comparison, less developed. This article offers three main contributions. First, it draws a clear distinction between two types of crystallisation: automatic and express. Second, it applies the theoretical literature on floating charges to crystallisation and examines the different meanings crystallisation takes under these theoretical frameworks. Finally, it makes an original argument on the effectiveness of express crystallisation clauses. The claim is that because a crystallised floating charge establishes the same proprietary interest as a fixed charge ab initio, the legal criteria necessary to create a fixed charge should also be necessary for the triggering of an express crystallisation clause to be effective in crystallising a charge.