Acid Yellow 7 is a dye solution mixture that is used for visualizing fingerprints and footwear impressions made in blood. Treated bloodstains fluoresce under blue/blue-green light. Suitable for non-porous surfaces only. Prior to staining with Acid Yellow 7, impressions must be fixed to prevent them from running and causing loss of detail when the Acid Yellow solution is applied. Fix with a 2% solution of 5-sulphosalicylic acid.