Physical Developer

Introduction

Physical Developer (PD) is a silver-based liquid reagent which reacts with lipids, fats, oils and waxes present in fingerprint residue. Physical Developer is a productive means of developing latent prints on porous objects; however, it is the last of the processes in the regular chemical sequence. Paper items are generally treated with DFO first if a Forensic Light Source is available, then with Ninhydrin. The items are processed with Physical Developer last. After each step, the developed latent prints should be evaluated and photographed, as the next step may obliterate the prints developed from the previous step. Physical Developer has been found to work well on numerous items, including:

• dry paper items
• clay fire bricks
• concrete/gesso statuary
• latex or rubber gloves
• both sides of adhesive tape
• wet paper or previously wet paper
• rayon or nylon clothing
• unfinished porcelain
• unfinished wood
• wooden knife handles
• items which have not been touched in years

Safety

Wear laboratory coats and nonporous gloves when using PD. Protective eye wear should be worn. Provide facilities in the immediate area for washing eyes and other affected areas if reagents are splashed or spilled. Wash affected areas thoroughly under cold running water. If any reagent is splashed into the eyes, thoroughly wash eyes with cold running water. Seek medical attention if soreness or other symptoms persist. If the reagent is repeatedly splashed over the hands or if the hands are immersed in the solution without wearing nonporous gloves, some individuals may develop an allergic skin reaction to n-dodecylamine and various detergents used in PD. This will occur most frequently with individuals who also exhibit skin reactions to household detergents. PD contains several reagents, such as ferric nitrate, which are irritants and slightly corrosive. Both the silver nitrate solution and the PD working solution are corrosive and toxic and will cause black staining on skin and clothing. NOTE: Material Safety Data Sheets advise that contact lenses should not be worn when working with chemicals.

Paper with an alkalinity factor above pH 7 is not suitable for processing with this PD solution. It will turn dark and the latent prints will be lost. Thermal FAX paper is an example of unsuitable paper.

Mixing Instructions

NOTE: Clean glassware (really clean!) must be used in solution preparation and processing. Glassware should first be washed with detergent and rinsed with tap water, then rinsed thoroughly with distilled or deionized water. If the glassware is dirty, silver will deposit in those areas and not on the evidence. Disposable plastic beakers and trays may be used to reduce the possibility of contamination.

Mix the 25 grams of Maleic Acid crystals in 1 liter of distilled water. This is for the pre-wash step. Store this in a clean, brown glass bottle. Be sure to label it properly.

Do not mix Physical Developer Solution A and Solution B together until you are ready to process evidence. The shelf life of the working solution is about 1-2 days. Only mix enough quantity of working solution from the two bottles to process the evidence you currently have. Shelf life of the unmixed chemicals should be at least six months. Store them in a refrigerator to improve the shelf life, but do not let them freeze. Sunlight and heat degrade the chemicals.

1. Example of measured quantities: Add 5 ml of Solution A (20% silver nitrate solution) to 90 ml of Solution B (reductant solution).
2. Stir working solution for approximately 1 minute with a clean glass or plastic stirring rod.

NOTE: If a greater volume of PD working solution is needed, remember for every 90 ml of Solution B, add 5 ml of Solution A. This is a working ratio of 18:1. If needed for a larger amount of evidence, the entire contents of both bottles (A & B) can be mixed together.

Use plastic photographic tongs or plastic forceps without serrated edges to remove articles from PD solution. Do not use metal tools. Do not poke or dent the paper items while they are submerged in Physical Developer. Handle items carefully even when wearing gloves. Dents made by metal forceps or tweezers and glove marks may cause deposits of silver which may obliterate usable prints.

Processing Instructions

Pour the Maleic Acid Pre-Wash into a clean glass or plastic tray. Pour the Physical Developer working solution into a second clean glass or plastic tray. Immerse the document in the Maleic Acid Pre-Wash for at least 5-10 minutes or until no more bubbles rise from the paper, whichever is LONGER. Drain momentarily and move the paper into the tray of Physical Developer solution. Gently rock the tray. Generally, latent prints begin to develop in approximately 5 minutes. Do not process for longer than 15 minutes for any one item. Keep in mind that latent prints can be overdeveloped or a background color may also develop and obscure the fingerprints.

After the specimen has been processed, rinse it in tap water. This can be done by placing another clean tray in a sink and allowing a continuous gentle flow of water to run into the tray. Rinse the specimen in the running tap water until excess stains are gone. The tap water should be clear as it runs out of the tray. The specimen must be thoroughly dry before prints can be conclusively evaluated. If a thoroughly rinsed and dried specimen exhibits low contrast prints, the specimen may be reprocessed. Prior to reprocessing, all identifiable latent prints should be photographed. Next, wash the specimen in distilled or deionized water to remove residual chlorine from the tap water. Place the specimen in the Physical Developer working solution to attempt to develop any weak prints. Rinse and dry as before, and reexamine the prints. PD prints may darken if the specimen is not thoroughly rinsed; therefore, prints should be preserved through photographic methods.

Regenerating PD

Processing large amounts of evidence may eventually exhaust the silver content in the solution. It will then be necessary to mix a new kit of Physical Developer or to regenerate the solution. Regenerate by adding an entire new bottle of Solution A, the silver concentrate. This regeneration process may only be done during a short time period. In other words, if you are processing many pieces of paper and suddenly no latent prints are developing, add a new bottle of Solution A, stir completely and continue processing. Do not save the solution and wait until the next day to do this regeneration process. It is recommended that the regeneration process is performed within a few hours of the original process.