text: A ninhydrin solution is commonly used by forensic investigators in the analysis of latent fingerprints on porous surfaces such as paper. The amino acids present in the minute sweat secretions that gather on the finger's unique ridges transfer to surfaces that are touched. Exposure of the surface to ninhydrin converts the amino acids into visibly colored products and thus reveals the print. The test solutions suffer from poor long-term stability, especially if not kept cold.
  To further enhance the ability of ninhydrin, a solution of 1,2-indandione and zinc chloride (IND-Zn) can be used prior to ninhydrin. This sequence leads to greater overall reaction of the amino acids, possibly by IND-Zn helping to release them from the surface for the subsequent ninhydrin reaction.