ISO 17972-4:2015 defines an exchange format for spectral measurement data of inks to provide a means to characterise spot colour inks to allow reliable printing and proofing of products that have been designed using these inks. Only isotropic (paper-like) substrates are within the scope of this part of ISO 17972 which is limited to application areas where the same ink and paper combination that has been characterised is used when printing. ISO 17972-4:2015 describes the use of a CustomResource element within the CxF framework to define a minimum and recommended set of data for exchange.