Use of an optimized 1,2-indanedione process for the development of latent prints*

1,2-Indanedione belongs to a class of compounds which have demonstrated great potential in the processing of latent prints, particularly in the area of fluorescence. However, variability in results achieved worldwide has precluded it from being used extensively. In order to isolate the cause of this variability, various components of the formulation were analyzed, including purity level of the indanedione, type of carrier solvent, and the use of ZnCl(2) both as a secondary application and incorporated into the reagent. Using a resultant optimized formulation (Ind-Zn), performance comparisons were then made in the areas of visible color development, fluorescence, and degree of substrate staining with those of 1,8-diazafluoren-9-one (DFO) for both fresh and aged prints. Moisture content of the paper substrates on which the prints had been deposited was measured and a correlation found with percentage ambient relative humidity (% RH). Determination of visible color and fluorescence as it corresponded to percentage moisture content allowed for defining critical threshold levels necessary for achieving optimal results. Correlating these values with % RH then allowed for the development of standard operating procedures for obtaining best possible print development. Through this work, it was determined that a 7.4% v/v formulation of Ind-Zn having petroleum ether as a carrier solvent yielded the most optimal results when processing methods optimized for % RH in the laboratory were utilized. Both initial color development and fluorescence were superior to that of DFO; prints developed with Ind-Zn were a minimum of 6.5 units dE* darker and more red than with DFO for all substrates tested. Processing with Ind-Zn on the majority of the substrates examined yielded fluorescence intensity values approximately four times greater than with DFO.