Bromophenol Blue as a Chemical Enhancement Technique for ...

Technical Note 

Bromophenol Blue as a Chemical 

Enhancement Technique for Latent 

Shoeprints 

Katelyn McNeil 1 

Wade Knaap 2 

Abstract: The enhancement of two-dimensional shoe impressions, 

where the matrix is soil, may best be approached using chemistry. 

Potassium thiocyanate, which reacts with iron particles in soil, is a 

generally accepted development medium used by forensic investigators. 

Bromophenol blue, a pH indicator that reacts with carbonates in 

soil, is used, but with less frequency, particularly in North America. 

This study compared both chemistries and their ability to enhance 

two-dimensional shoe impressions deposited from a variety of soil 

samples on varying substrates. Bromophenol blue, although determined 

to be an inappropriate enhancement technique for brown paper 

samples, provided significantly more detailed enhancement than potassium 

thiocyanate with other tested substrates, including plastic and 

linoleum. 

Introduction 

The documentation and preservation of two-dimensional 

shoeprint impressions can be difficult. Impressions can be left in 

various substances (e.g., dust, blood, mud), which makes details 

difficult to detect. Before a shoeprint can be processed, it must 

be photographed, but often this photograph lacks sufficient 

contrast. Chemical enhancement techniques provide increased 

contrast between the shoeprint and the background, allowing 

photographs to document more detail. These enhancement 

techniques can be valuable, but there is little research available 

to assess their effectiveness. 

1 University of Toronto Mississauga, Ontario, Canada 

2 Forensic Identification Services, Toronto Police Services, Ontario, 

Canada 

Received December 13, 2010; accepted April 12, 2011 

Journal of Forensic Identification 

62 (2), 2012 \ 143

Potassium thiocyanate was first introduced in the United 

States in 1994 [1]. Someha acknowledged Junichi Murao as the 

individual who developed the technique in 1957. This technique 

is regarded as the most effective chemical enhancement 

technique for dusty and muddy footwear impressions regardless 

of the substrate on which it is deposited [2]. Potassium thiocyanate, 

routinely used by the Ontario Provincial Police, reacts 

with metal ions in soil, particularly iron, to cause a bright red 

coloration, depending on ferric ion concentration in the soil [3]. 

Bromophenol blue, developed as a forensic identification 

technique in 1996, has been used with great success in Israel 

as a chemical enhancement technique [4]. Bromophenol blue 

is a pH indicator with a transition range of pH 3 to 4.6. In the 

acidic form, it appears yellow and in the basic form, it appears 

blue. The enhancement of bromophenol blue can be improved 

by applying steam [4]. Bromophenol blue reacts with carbonates 

in the soil [4] as well as with amino acids [3] and has been 

found to be more effective than other chemical enhancement 

techniques when calcium carbonate is a major component in the 

soil [5]. Other studies have used gel lifters to recover shoeprints 

and have then treated them with bromophenol blue. Because 

the white adhesive lifter provides better contrast between the 

background and developed impression, it is easier to apply vapor 

directly after if required, and this removes the issue of enhancement 

of the background as well [5]. 

The aim of the current study is to assess the usefulness of 

bromophenol blue on soils from several locations in Ontario, 

Canada. Also, the present study examines the enhancement 

abilities of bromophenol blue and compares them to potassium 

thiocyanate. It is hypothesized that bromophenol blue is 

an effective chemical enhancer for soil shoeprint deposit. The 

enhancement chemistries – bromophenol blue and potassium 

thiocyanate – were tested on various soil samples and substrates. 

Method 

Ten soil samples were collected from several locations 

throughout southern Ontario to allow for comparison: Ottawa, 

Mississauga, Brampton, Scarborough, Port Perry, Oak Ridges, 

and four areas in Toronto (Lakeshore at Sunnyside Park; St Clair 

Avenue West and Keele Street; Toronto Iron Works at Eastern 

Avenue and Caroline Avenue; and banks of the Don River). The 

soil samples were all placed in separate cardboard hand-gun 

boxes, air-dried, and broken into smaller dustlike particles. 


144 / 62 (2), 2012

The left shoe of a pair of size 8 women’s Sketcher shoes 

was used to make all shoe impressions. Individual characteristics 

were created by the researcher by cutting the outsole and 

by the insertion of a thumb tack. For comparison purposes, a 

control shoeprint (Figure 1) was created by dusting a greasy 

shoeprint impression with black magnetic fingerprint powder. 

The enhanced impression was then analyzed, with eight individualizing 

characteristics being noted. The control print was then 

copied onto an acetate overlay. For all test impressions, the same 

individual (wearer) deposited each impression with a similar 

stepping technique (i.e., rolling from heel to toe) and application 

force to provide replication consistency. Experimental impressions 

were made by stepping into a hand-gun box containing a 

sample soil collection. Excess soil was shaken off of the outsole 

prior to stepping on each substrate. All experimental impressions 

were deposited in the same fashion as to approximate a realistic 

walking pattern. All impressions were photographed before 

enhancement using lighting techniques to capture maximal 

detail. This was completed to ensure that there were no significant 

differences in detail in the latent shoeprint impressions. If 

experimental impressions were smudged or had an otherwise 

inappropriate level of detail, impressions were excluded from 

the study before treatment with enhancement chemistries. 

Figure 1 

Control shoeprint with the eight individual characteristics identified. 


62 (2), 2012 \ 145

Impressions on brown paper were photographed using 

overhead f luorescent lighting; impressions on plastic and on 

linoleum were photographed with oblique white light generated 

from a Luma-Lite (Payton Scientific Inc., Buffalo, NY). For 

brown paper and plastic substrate samples, six impressions were 

made, whereas only four impressions were made on linoleum. 

Half of the impressions were sprayed with bromophenol blue 

and the other half were sprayed with potassium thiocyanate. 

All enhanced prints were photographed. Prints enhanced with 

bromophenol blue were steamed for maximal contrast and then 

re-photographed. This technique added extra moisture to the soil 

so that the enhancement could occur. 

Both of the enhancement chemistries were prepared at the 

Toronto Police Forensic Identification unit. To make potassium 

thiocyanate, 15 g of potassium thiocyanate (Alphachem Ltd. 

Mississauga, Ontario) was added to 120 mL of acetone and 15 

mL of water. In a separate beaker, 1 mL of concentrated sulfuric 

acid was added to 9 mL of water. Upon mixing the dilute acid 

and potassium thiocyanate mixture, a solute formed. Once the 

solute settled, an eye dropper was used to transfer the top layer 

to a spray bottle. For the purposes of this study, a fine mist was 

necessary to be produced. To generate this spray, the Kitchen 

Spritzer (Pampered Chef, Addision IL) was used (Figure 2). 

This spray bottle uses a hand pump to create pressure so that a 

fine mist can be generated. The bottle was pumped until there 

was resistance against the pumping (approximately three full 

pumps). A small amount of mist was released before being 

sprayed onto the experimental impressions. The bromophenol 

blue (Alphachem Ltd. Mississauga, Ontario) was prepared using 

as a solution of 1% (w/v) bromophenol blue in a solution of 5% 

water in methanol. 

For the analysis of the experimental prints, the acetate 

overlay was used to make pointwise comparisons on a four-point 

scale: 0 to 3. A score of 0 was used to denote the absence of the 

individual characteristic or if the enhancement obscured the 

detail, and 1 was used to denote the presence of the individual 

characteristic but that it lacked identifying detail. Both 0 and 

1 lacked sufficient detail to make an identification and were 

classed as nonconclusive. A score of 2 was used when the 

individual characteristic was present and defined, and a score 

of 3 was assigned when individual characteristics were present, 

well defined, and showed clear enhancement. Both a 2 and a 3 

had sufficient detail for an identification to be made. A paired 

t-test was used to test the means of between nonconclusive and 


146 / 62 (2), 2012

Figure 2 

Kitchen Spritzer. 

identification between potassium thiocyanate and bromophenol 

blue. For the t-test, a score of 0 or 1 was given a score of 0, and 

a score of 2 or 3 was given a score of 1 for statistical purposes. 

Qualitative observations were also made about the level 

of enhancement. Because of the nature of the enhancement 

techniques, they may not have worked on all of the soil types. A 

classification of “enhanced” or “did not react” was made with 

each soil type for each enhancement method (potassium thiocyanate 

and bromophenol blue). A scale from -1 to 3 was used to 

assess the enhancement. A score of -1 was given if there was 

a deterioration of the print (e.g., the enhancement chemistry 

reacted with the substrate, obscuring the detail of the shoeprint 

impression). A score of 0 was given when the print was not 

enhanced (e.g., the shoeprint impression appeared the same 

before and after the enhancement chemistry was applied). A 

score of 1 was given for a somewhat enhanced shoeprint impression 

(e.g., the chemistry reacted with the soil but resulted in 

limited enhancement). A score of 2 was given when the shoeprint 

impression was enhanced (e.g., there was contrast between the 

background and the enhanced shoeprint impression). A score of 

3 was given when the print was very much enhanced (e.g., there 

was very strong, clear, distinct enhancement of the shoeprint 

impression). Also, because of the nature of the substrates, a 

judgment about whether the enhancement technique was appro- 


62 (2), 2012 \ 147

priate also was made. For the bromophenol blue, the substrate 

was deemed to be acceptable if the background turned yellow 

and the soil turned blue, but if the background turned blue, then 

it was unsuitable. For potassium thiocyanate, if the soil turned a 

red to pink color and the background did not turn significantly 

red to pink, then it was considered to be appropriate for the 

substrate. Also, any particular characteristics or interactions 

between liquid and substrate were also noted. 

Results and Discussion 

Both bromophenol blue and potassium thiocyanate reacted 

with all of the soil samples from the Toronto areas. Bromophenol 

blue reacted with the brown paper substrate, causing the brown 

paper to turn blue, which obscured the footwear impression. It 

has been previously noted that a formulation of bromophenol 

blue that consists of too much water can cause the background to 

enhance [4]. Perhaps a different formulation of bromophenol blue 

would be effective in enhancing shoeprints on paper samples, 

though it is noted that white paper has previously been found to 

react [4]. Also, the steaming step of the enhancement of bromophenol 

blue may be unnecessary in humid climates because it 

introduces extra moisture, which may cause it to overreact. The 

soil samples in the present study lacked moisture and, as a result, 

adding extra moisture benefited the enhancement, but often the 

samples reacted before the steam was applied. Bromophenol blue 

used on the plastic and on the linoleum ranged from “somewhat 

enhanced” to “very much enhanced”, whereas when it was used 

on brown paper, there was a deterioration of detail. Potassium 

thiocyanate was effective at enhancing all substrates tested, but 

it tended to have a weaker contrast compared to bromophenol 

blue. Potassium thiocyanate ranged from a level of “unaltered” 

to a level of “very much enhanced” but often gave minimal 

enhancement. Table 1 lists the qualitative ratings of level of 

enhancement. Although qualitative analysis is subjective and 

different conclusions can be drawn even among experts [6], 

the trend of bromophenol blue having a stronger enhancement 

contrast is evident. 


148 / 62 (2), 2012

Bromophenol Blue Potassium Thiocyanate 

Soil Paper Plastic Linoleum Paper Plastic Linoleum 

St Clair and Keele 0.67 2.5 2 1.67 2 0.5 

Don River 0.33 2.67 1.5 1.33 1.67 0.5 

Toronto Iron Works -1 1.33 1 1 1 1 

Port Perry -1 2 1.5 1.67 1 1 

Scarborough -1 1.67 2 1.33 1.33 1 

Ottawa -1 1.33 1 1.33 1.67 1 

Lakeshore -1 2 1 2 2 1 

Mississauga -1 1.67 1.5 2.33 1.67 1 

Oak Ridges -1 1.33 1.5 1.67 2 2.5 

Brampton -1 1 1 1.33 1 1 

Average -0.7 1.75 1.4 1.67 1.53 1.05 

Table 1 

Average qualitative ratings of level of enhancement. 

From paired t-test analyses it was found that when all of the 

substrates were considered, the levels of enhancement of bromophenol 

blue and potassium thiocyanate were not significantly 

different [t(78) = 0.49, P < 0.622], but when the brown paper 

was excluded, bromophenol blue enhanced individual details 

significantly better than potassium thiocyanate [t(47) = 4.78, P 

< 0.001]. 

When analyzing specific substrates, potassium thiocyanate 

enhanced detail significantly better than bromophenol blue on 

brown paper [t(28) = 7.29, P < 0.001], but bromophenol blue had 

a significantly higher level of detailed enhancement than potassium 

thiocyanate on linoleum [t(19) = 3.09, P < 0.006] and plastic 

[t(26) = 4.27, P < 0.001]. Plastic gave the best level of detail 

for both bromophenol blue and potassium thiocyanate, whereas 

the enhancement of latent shoeprints on brown paper treated 

with bromophenol blue had the lowest level of enhancement. 

These results are depicted in Figure 3. Overall, bromophenol 

blue had more three-point enhancements, identifying level of 

detail, than the potassium thiocyanate. See Figure 4 and Figure 5 

for examples of enhancement on the plastic substrate using the 

same soil sample with bromophenol blue and with potassium 

thiocyanate, respectively. 

An analysis of individual detail enhancement of each of the 

soils was also conducted. The level of enhancement of individual 

detail from the pointwise comparisons was not significantly 

different between soils from Mississauga, Lakeshore, Ottawa, 

Brampton, Don River, St Clair Avenue and Keele Street, and 

Toronto Iron Works even when the overenhanced paper samples 

treated with bromophenol blue were removed from the analy- 


62 (2), 2012 \ 149

sis. Potassium thiocyanate had a significantly higher level of 

individual detail enhancement on the pointwise comparison than 

bromophenol blue [t(7) = 2.45, P < 0.05] for the Oak Ridges soil. 

When the overenhanced bromophenol blue on paper samples 

were removed from the analysis, bromophenol blue and potassium 

thiocyanate performed equally. The enhancement of soil 

from Scarborough was approximately equal when overenhanced 

bromophenol blue brown paper samples were included, but when 

they were removed from the analysis, then bromophenol blue 

gave a significantly better enhancement of detail than potassium 

thiocyanate [t(4) = 5.31, P < 0.006]. Port Perry soil was 

not found to have significantly different ratings of enhancement 

of individual detail until the overenhanced bromophenol blue 

on paper samples were removed from the analysis, and then 

bromophenol blue performed significantly better than potassium 

thiocyanate [t(4) = 8.55, P < 0.001]. See Table 2 for a list of 

means of enhancement rating for each soil sample. 

Soil 

Bromophenol 

Blue 


150 / 62 (2), 2012 

All Substrates Plastic and Linoleum Only 

Potassium 

Thiocyanate 

Bromophenol 

Blue 

Potassium 

Thiocyanate 

St Clair and Keele 0.542 0.208 0.750 0.208 

Don River 0.469 0.594 0.650 0.550 

Toronto Iron 

Works 

0.250 0.281 0.375 0.275 

Port Perry 0.391 0.250 0.625* 0.225* 

Scarborough 0.453 0.281 0.725* 0.275* 

Ottawa 0.313 0.375 0.500 0.375 

Lakeshore 0.297 0.500 0.475 0.500 

Mississauga 0.359 0.422 0.525 0.350 

Oak Ridges 0.359* 0.594* 0.575 0.700 

Brampton 0.359 0.359 0.575 0.300 

* Indicates significant difference 

Table 2 

Mean of individual detail enhancement of soil samples. 

Though a variety of chemistries can be valuable tools when 

it comes to enhancing impressions left at crime scenes, they 

also have inherent limitations that have to be acknowledged so 

that they can be minimized. When administering the chemistry 

to the substrate in question, sufficiently fine mist is necessary 

to ensure that water droplets do not form. This is especially 

important on nonporous surfaces, such as plastic or linoleum, 

because if droplets form, the detail of the shoeprint is obscured. 

Also, caution has to be taken that too much of an enhancement 

chemistry is not sprayed onto the shoeprint impression because 

this can cause running, which can obscure detail in a print.

Figure 3 

Comparison of enhancement between chemistries and substrates. 

(* Indicates significant difference.) 

Figure 4 

Bromophenol blue enhancement of soil from St Clair and Keele on plastic. 

Figure 5 

Potassium thiocyanate enhancement of soil from St Clair and Keele on 

plastic. 


62 (2), 2012 \ 151

Some limitations of the present study are that the formulation 

of the bromophenol blue reacted with the brown paper, which 

caused the background to enhance as well. A commercially 

made aerosol container of bromophenol blue (Bromphenol Mix, 

#36729, Evident, Inc., Union Hall, VA) is available and preliminary 

tests of it showed that it did not react with the brown paper 

substrate. The aerosol container would be ideal in that it emits a 

fine mist that does not cause water droplets to form. It is easily 

transportable and premixed, which makes it practical to use. One 

drawback of the commercial bromophenol blue spray is that it 

is costly. It costs approximately $90 CDN, whereas buying the 

bromophenol blue crystals and mixing it in the lab costs approximately 

the same but yields 25 times the amount. Bromophenol 

blue is easily prepared, whereas the potassium thiocyanate 

formulation is more complex, involving a separation step. A 

second limitation of the study is that the same shoe was used 

for each impression made. This allows the individual characteristics 

of the print to be consistent across all the samples, but 

it introduces the possibility of contamination of the soil types. 

The bottom of the shoe was cleaned thoroughly before a new soil 

sample was used in attempts to reduce contamination. Another 

limitation of the study is the limited number of substrates used. 

Although a textured linoleum, a nonporous plastic surface, and 

a porous surface (paper) were used, other common substrates 

should also be tested. 

Suggestions for future research include testing the effectiveness 

of bromophenol blue on a variety of substrates so 

that potential deleterious reactions between the chemistry and 

substrate are established. Also, although the soil samples were 

thought to be representative of Toronto and surrounding areas, 

other areas may have different soil compositions that may not 

react appropriately with the bromophenol blue. Even though a 

sample was used from Ottawa, it was only a single sample and 

may not be representative of that area. 

Conclusion 

Overall, bromophenol blue is an effective chemical enhancement 

technique for use on soils in the area tested. The current 

research supports that of Glattstein et al. [4]. Bromophenol 

blue performs equally or better than potassium thiocyanate on 

enhancing individual details and gives a better level of contrast. 

The contrast given from bromophenol blue is clear because the 

background turns yellow and the latent shoeprint, the soil, turns 


152 / 62 (2), 2012

lue. One drawback of bromophenol blue is that it is not suitable 

for use on all substrates. 

For further information, please contact: 

References 

Katelyn McNeil 

88 Mapleburn Drive SE 

Calgary AB 

T2J1Y6 

Canada 

katelyn.mcneil@live.ca 

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Footwear and Tire Impressions in Japan. In Proceedings 

of the International Syposium on the Forensic Aspects of 

Footwear and Tire Impression Evidence. Federal Bureau 

of Investigation, Laboratory Division, U.S. Department of 

Justice, U.S. Government Printing Office: Washington D.C., 

1994. 

2. Davis, R. J. A Systematic Approach to the Enhancement 

of Footwear Marks. Canadian Society of Forensic Science 

Journal 1988, 21, 98–105. 

3. Theeuwen, A. B.; van Barneveld, S.; Drok, J. W.; Keereweer, 

I.; Lesger, B.; Limborgh, J. C.; Naber, W. M.; Schrok, R.; 

Velders, T. Enhancement of Muddy Footwear Impressions. 

For. Sci. Int. 2001, 119 (1), 57–67. 

4. Glattstein, B.; Shor, Y.; Levin, N.; Zeichner, A. pH Indicators 

as Chemical Reagents for the Enhancement of Footwear 

Marks. J. For. Sci. 1996, 41 (1), 23–26. 

5. Shor, Y.; Vinokurov, A.; Glattstein, B. The Use of an Adhesive 

Lifter and pH Indicator for the Removal and Enhancement 

of Shoeprints in Dust. J. For. Sci. 1998, 43 (1),182–184. 

6. Majama, H.; Ytti, A. Survey of the Conclusions Drawn of 

Similar Footwear Cases in Various Crime Laboratories. For. 

Sci. Int. 1996, 82 (1), 109–120. 


62 (2), 2012 \ 153

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