Rees and Schwartz, The Effectiveness of Liqui-Drox and a Comparison to Other Adhesive-Side Processes on a Variety of Tapes
January 2003 - Volume 5 - Number 1
Research and Technology
The Effectiveness of Liqui-Drox and a Comparison to Other Adhesive-Side Processes on a Variety of Tapes
Alison S. Rees
Physical Scientist/Forensic Examiner
Rebecca L. Schwartz
Latent Print Units
Federal Bureau of Investigation
This study evaluates the effectiveness of Liqui-Drox as a process for developing latent prints on the adhesive side of a variety of types of tapes and compares it to four standard processes: alternate black powder, ash gray powder, gentian violet, and sticky-side powder at two lengths of storage time. Results of the comparisons and changes in recommended processing procedures are presented here.
Crime scenes often contain evidence that includes some type of adhesive tape, especially scenes where the crime involves abductions, drugs, and explosive devices. This evidence requires fingerprint examination. Whereas the methods used to process the nonadhesive side of tape are well-known, the ability to develop prints on both sides of tape could be very important to an investigation. As a result, procedures for processing the adhesive side continue to develop.
The FBI Latent Print Units currently use several techniques to process the sticky side of tape: alternate black powder, ash gray powder, gentian violet, and sticky-side powder. An extensive study using many different types of tape was done to determine which one of these processes produces the most consistent ridge detail on each individual type of tape. The results of this study are documented in the Processing Guide for Developing Latent Prints (Trozzi et al. 2001). In some cases, where two processes yielded equally sufficient development, an alternate process is listed.
Specialists in the FBI Latent Print Units have designed an additional technique, Liqui-Drox, to be used on both the adhesive and nonadhesive sides of tape (Hollars et al. 2000). Liqui-Drox is a fluorescent process that has been proven to be effective on both sides of dark tapes. However, its effectiveness had not been evaluated on light-colored tapes, nor had it been compared to other adhesive-side processes.
The purpose of this study was twofold. The first was to determine if Liqui-Drox is sufficiently productive to be listed as a standard process for adhesive surface techniques in the updated Processing Guide for Developing Latent Prints. The second was to compare Liqui-Drox with the process that is currently recommended for each type of tape and determine which gives better results.
Fingerprints were placed on two sets of different types of tape. The sets were processed at two different times. Both Liqui-Drox and the techniques listed in the Processing Guide for Developing Latent Prints were used in this study. Developed fingerprints were photographed and analyzed in order to compare the processes.
This study consists of two parts, A and B. Specimens in Part A were processed approximately two minutes after the fingerprints were deposited on the tape. In Part B, fingerprints were deposited on the tape, then the tape was placed adhesive-side down on clean acetate and stored in an evidence locker for one month. At the end of the month, the tape was removed from the acetate and processed for fingerprints. Twenty-five tapes of varying colors, brands, and widths were used in this study (Table 1). Twelve pieces of each type of tape, each nine inches long, were divided into four segments. Fingerprints were placed successively in each segment with no deliberate transfer medium on the finger. Six pieces of each tape were used in Part A, and six were used in Part B. In both parts, three pieces of each type of tape were processed with Liqui-Drox. The other three pieces were processed with the techniques suggested in the Processing Guide for Developing Latent Prints. As a result, each part consisted of a total of 150 specimens and 600 fingerprints.
The following five mixing and processing procedures were used to develop fingerprints on the tape. Details can be found in the Processing Guide for Developing Latent Prints.
- Alternate Black Powder - In a small dish, mix one teaspoon of Lightning® black powder and 40 drops of a 50/50 solution of distilled water and Liqui-NoxTM. Stir the powder and the solution together until it is the consistency of shaving cream with small bubbles. Brush the solution onto the tape specimens with a camel-hair brush. Wait 30-60 seconds; rinse with cold tap water.
- Ash Gray Powder - Mix one teaspoon of ash gray powder with enough undiluted Photo-FloTM 600 to make a solution that is the consistency of thin paint. Using a camel-hair brush, paint the solution onto the tape and allow it to sit for 30-60 seconds before rinsing with cold tap water.
- Gentian Violet - Dissolve one gram of gentian violet in one liter of distilled water. Place the tape specimens in the solution for 1-2 minutes, then rinse with cold tap water.
- Liqui-Drox - Manually mix 200 ml of Ardrox P-133D, 400 ml of Liqui-NoxTM, and 400 ml of distilled water until the solution has a thick, milky-yellow consistency. With a camel-hair brush, paint the solution onto the tape, wait 10 seconds, then rinse the specimens free of the solution with cold tap water. Dry the specimens and examine them under a long-wave ultraviolet light (365 nm). Because prints developed with Liqui-Drox begin to fade after 12 hours and cannot be regenerated, the specimens should be photographed as soon as possible to document the presence of any developed fingerprints.
- Sticky-Side Powder - Mix one teaspoon of sticky-side powder with Photo-FloTM 100 solution (Photo- FloTM 200 diluted 50/50 with distilled water) until the solution has a consistency of thin paint. Using a camel-hair brush, paint the solution onto the surface of the tape. After 30-60 seconds, rinse the specimens under cold tap water.
All tape specimens with developed fingerprints were prepared for photography by pinning the ends of the air-dried specimens to cardboard and placing them in an empty box to prevent the tape from sticking to itself or becoming contaminated. All specimens were photographed with a Polaroid® MP4 camera. Kodak Ektapan 4x5 sheet film was used to photograph specimens that required long-wave ultraviolet light (365 nm). The remaining specimens were photographed with Kodak Pro Copy 4x5 sheet film. When it was necessary to reverse the color of photographed specimens, Kodak Commercial 4x5 sheet film was used.
Four latent print examiners analyzed and rated each photographed fingerprint based on the number of level two detail features (i.e., dots, ending ridges, and dividing ridges) and the following criteria: contrast, sharpness, and area. Contrast, sharpness, and area were given a score between 1 (poor) and 5 (excellent). The number of level two detail features and the criteria scores for each fingerprint were averaged in order to compare Liqui-Drox to the other processing techniques. Tape specimens with no fingerprint development were recorded as zeros and not analyzed.
Liqui-Drox did not develop fingerprints on 11 of the tapes: clear-textured tape, white cloth tape, white decorate and repair tape, off-white masking tape, yellow heavy-duty tape, green heavy-duty tape, white duct tape, dark brown duct tape, black duct tape, clear with white stripes strapping tape, and white transparent packing tape. As a result, no further analysis was done on these types of tape, and the recommended processing method was left unchanged.
With the remaining 14 tapes, there were a possible 168 total pieces of tape and 672 prints. Of these, a total of 82 tape specimens with 326 fingerprints were photographed for Part A, and 57 tape specimens with a total of 238 fingerprints were photographed for Part B. The remaining specimens did not contain any developed fingerprints to be photographed.
Results of the evaluations of the prints on the remaining 14 types of tape differ considerably between those specimens that were processed immediately as Part A and those that were adhered to acetate for one month prior to their development as Part B (Table 2). In two cases, after being stored one month, the clear and the cloudy ScotchTM tape specimens were not successfully removed from the acetate. Removal was first attempted with heat from a hair dryer, but the tape ripped into several strips. Submerging the acetate in liquid nitrogen caused the acetate to break into pieces with the tape removal attempt. Therefore, results for the ScotchTM tapes are based only on the fingerprints developed within two minutes after fingerprint placement (Part A).
Averages of those tapes that were processed with alternate black powder and Liqui-Drox indicate that Liqui-Drox worked as well as or better than the alternate black powder, except in the case of gray duct tape (Table 2). Thus alternate black powder is far superior to Liqui-Drox in developing prints on gray duct tape. There is a substantial improvement in development on clear ScotchTM tape, red transparent packing tape, and green transparent tape when using the Liqui-Drox technique.
In comparison to ash gray powder, Liqui-Drox performed equally as well on clear packing tape and black heavy-duty tape. In the case of black decorate and repair tape, there was minimal development of prints using Liqui-Drox, but significant development using ash gray powder. Liqui-Drox was superior to ash gray powder on black vinyl electrical tape.
The development of prints on the orange transparent tape was better using Liqui-Drox than with sticky-side powder. Fingerprints on the cloudy ScotchTM tape were scored slightly higher using Liqui-Drox over gentian violet.
When the tape was removed from the acetate after one month of storage as Part B, the processing and developing results were considerably different than observed in Part A. In comparing alternate black powder to Liqui-Drox in Table 2 Part B, fingerprints developed with alternate black powder were scored much higher in all categories on the yellow, red, and green transparent tape, and gray duct tape. No prints were developed on the gray duct tape using Liqui-Drox, although some did develop using alternate black powder. Fingerprints that developed on the light brown packing tape were rated slightly higher using the alternate black powder technique, although the Liqui-Drox method also yielded high-quality fingerprints. In the case of the blue transparent packing tape, there was no difference in the two processing techniques. In the case of the dark brown packing tape, Liqui-Drox developed better prints than alternate black powder.
Comparison of ash gray powder and Liqui-Drox on the aged prints indicates that ash gray powder developed better fingerprints than the Liqui-Drox on clear packing tape, black heavy-duty tape, black decorate and repair tape, and black vinyl electrical tape. In fact, no prints were developed with Liqui-Drox on the black vinyl electrical tape, whereas significant development was achieved using ash gray powder. Although the rating scores were higher using ash gray powder, good prints were still developed using Liqui-Drox on clear packing tape and black heavy-duty tape.
Similar to Part A, the fingerprints placed on the orange transparent packing tape were developed with better quality and quantity using Liqui-Drox than with sticky-side powder.
As stated above, the clear and cloudy ScotchTM tapes were not successfully removed from the acetate; therefore, no results are reported.
Overall in Part A, three tapes, clear ScotchTM, dark brown packing, and orange transparent packing, had better immediate fingerprint development (i.e., a greater number of level two detail features, better contrast and sharpness, and more area) with Liqui-Drox than with the method currently recommended. The Liqui-Drox fingerprints on the dark brown packing and orange transparent tape were rated higher in Part B also, but as mentioned above, no clear ScotchTM tape-aged specimens were able to be processed.
In examples where Liqui-Drox developed better fingerprints when the tape was processed within two minutes after placement, but yielded lower results at the end of one month, Liqui-Drox is listed as an alternate method. The tapes in this category include yellow, red, and green transparent packing tape; light brown transparent tape; clear packing tape; and black heavy-duty tape. Liqui-Drox is listed as an alternate for cloudy (standard) ScotchTM tape because the fingerprints developed with Liqui-Drox and the current method (genetian violet) had similar averages.
Although Liqui-Drox is not listed as the standard method for developing latent prints on black vinyl electrical tape, it is standard procedure at the FBI to use Liqui-Drox on both the adhesive and nonadhesive sides of the tape after the nonadhesive side has been processed by cyanoacrylate fuming. If no latent prints are developed on the adhesive side with Liqui-Drox, ash gray powder should be used as a follow-up.
It is important to note that processing with one adhesive-side method does not preclude additional processing with another adhesive-side method.
Based on the results of this study, Table 1 reflects the changes and addition of Liqui-Drox to the original Tape Chart by Method found in the Processing Guide for Developing Latent Prints.
Liqui-Drox is effective enough to be used as a standard process for immediate development of latent prints on the adhesive side of clear ScotchTM tape, dark brown packing tape, and orange transparent packing tape. However, one month after the storage of tape on acetate, Liqui-Drox has reduced effectiveness. It can also be used as an alternate method on some tapes. Because prints developed with Liqui-Drox will fade with increased exposure to long-wave ultraviolet light, they should be photographed as soon as possible to document the prints.
This paper would not have been possible without the assistance of Fingerprint Specialists Kenneth M. Getz, Jacob F. Holmes, IV, James N. Hudson (ret.), and Supervisory Fingerprint Specialist Richard L. Leas, who evaluated the photographs; Physical Scientist Heather Krohn, who assisted wit the making and processing specimens; and former FBI Latent Print Photographer Amanda Butler, who photographed and printed all developed prints.
Hollars, M. L., Trozzi, T. A., and Barron, B. L. Development of latent fingerprints on dark-colored sticky surfaces using Liqui-Drox, Journal of Forensic Identification (2000) 50:357-362.
Trozzi, T. A., Schwartz, R. L., and Hollars, M. L. Processing guide for developing latent prints, Forensic Science Communications [Online]. (2001). Available: http://www.fbi.gov/hq/lab/fsc/backissu/jan2001/lpu.pdf