of Liqui-Drox and a Comparison to Other Adhesive-Side Processes
on a Variety of Tapes
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.
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.
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.
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.
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.
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
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.
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.
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.
- 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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
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
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