Although the process is time consuming, using Physical Developer when other methods have failed could be the factor that helps solve a case.

On porous materials, a reaction occurs between the lipids, fats, oils, and waxes found in sebaceous sweat and the silver-based liquid reagent known as Physical Developer (PD) to produce a silver-gray deposit visible to the naked eye. Since these sebaceous components are not soluble in water, the PD latent print development technique is particularly useful on wet paper or paper that has previously been wet. When the amino acids in fingerprints have been washed away or failed to react with Ninhydrin, 1,2- Indanedione, or DFO; processing with PD may still produce identifiable latents. However, PD is time-consuming, expensive, destructive, and has a short shelf life. Therefore, one should only utilize PD as a final process in circumstances where it will be the most effective.

This preliminary study consists of comparisons made by the Canyon County Sheriff’s Office Crime Lab in Caldwell, Idaho, between a commercially, premixed PD kit and PD prepared in the laboratory. In addition to price determinations, three different types of paper were subjected to extended periods of environmental conditions prior to processing.

MATERIALS AND METHODS
The paper samples consisted of white printer paper, yellow lined notebook paper, and newspaper touched by several donors with their fingers and palms. One donor applied a full palm print to the center of each paper while the others applied fingerprints randomly to various areas. These latter prints were left unmarked so that the papers would be treated as though they were actual evidence. One sample of each type was then placed in one of two environmental conditions.The first set was placed in a drawer and allowed to age protected for approximately one month. The second set was exposed to the outdoor elements including snow, rain, wind, and sun for approximately seven hours and then allowed to dry indoors. Finally, each sample was cut in half for the two separate treatments and labeled as shown in Table 1.

The first step in either protocol involved soaking the papers in a slightly acidic pre-wash for at least five minutes to neutralize any alkaline binders and fillers which react strongly with PD. A Maleic Acid Pre-treatment Solution was prepared by stirring 50 g of maleic acid into 2 L of distilled water before transferring it to a clean plastic tray.

In the second step, the samples were removed from the prewash, placed in a clean glass tray containing PD, and soaked with agitation for approximately 15 minutes. An electric rocker was used to gently tilt the tray back and forth. The commercially prepared kit required combining one part (5 mL) of the 20% silver nitrate Solution A with eighteen parts (90 mL) of the reductant Solution B.