INTERNSHIP

Allison Fuchs

Physical Developer

Tyvek

THE COMPARISON OF A LOWER GRADE

SILVER NITRATE TO THE CURRENT

STANDARD GRADE TO PRODUCE A MORE

COST-EFFECTIVE PHYSICAL DEVELOPER

SOLUTION

INTRODUCTION

Physical developer

develop water insoluble portion of latent fingerprints on

porous surfaces

Silver ions deposited onto the fingerprint

Reduced by ferrous ions

Surfactant surrounds the silver particles

Silver nitrate

Recent price increase

Lower grade- economical, but more impurities

CHEMICAL GRADES

Used to indicate the purity of the chemical

A.C.S- meets the American Chemical Society

Standards

U.S.P.- meets U.S. Pharmacopeia requirements

acceptable for drug, medicinal, food, and laboratory use

Technical- lowest purity

industrial or commercial use

not pure enough for drug, medicinal, or food use

SAMPLES

101 Depletion Series strips

6 fingerprints each

Sebaceous

Ten Donors

4 females, 5 males, 1 unknown

4 females, 6 males

Substrates

Copy paper

Recycled copy paper

Lined paper

Express newspaper

Washington Post newspaper

Manila paper

Kraft paper

SOLUTIONS

Malic Acid Solution- 25g malic acid in 1L RO-DI

water

Physical Developer Solution- 900mL redox

solution, 40mL detergent solution, 50mL

appropriate 20% w/v silver nitrate solution

Redox Solution

80g ferrous ammonium sulfate + 20g of citric acid in 900mL

RO-DI water + 30g of ferric nitrate

Detergent Solution

3g n-dodecylamine acetate + 3mL Tween 20 in 1 liter RO-DI

water

Silver Nitrate Solution

20g appropriate silver nitrate in 100mL RO-DI water

METHOD 1

U.S.P grade silver nitrate and A.C.S grade silver

nitrate

Depletion series cut in half

RO-DI water wash for 5 minutes

Malic acid solution wash for 20 minutes

Appropriate PD solution wash for 20 minutes

Triple rinsed with tap water

Dried with a belt dryer

METHOD 2

Same procedure as Method 1

Technical grade silver nitrate replaced U.S.P. grade

silver nitrate

COMPARISON

Scale 1

0- No detail

1- Small amount of detail (~

< 1/4 of fingerprint)

2- Some amount of detail

(~ 1/4 – 1/2 of fingerprint)

3- Good amount of detail (~

1/2 – 3/4 of fingerprint)

4- Great amount of detail (~

3/4 - complete fingerprint)

A- No development

B- Light development

C- Dark development

COMPARISON

Scale 2-Fingerprint

Examiner

0- Not identifiable

1- Identifiable

+2= Lower grade side

much better

+1= Lower grade slightly

better

0= Sides equal

-1= Standard grade side

slightly better

-2= Standard grade side

much better

* = no fingerprint present

on either side

RESULTS- METHOD 1

Scale 1

Total number of fingerprints-

606

U.S.P side rated the same as

A.C.S. side- 456

U.S.P side rated higher than

A.C.S side- 98

U.S.P side rated lower than

A.C.S. side- 52

U.S.P. side lower- 9%

Scale 2

Undetermined USP ACS

RESULTS- METHOD 2

Scale 1

Total number of

fingerprints- 600

Technical side rated the

same as A.C.S. side- 468

Technical side rated higher

than A.C.S side- 66

Technical side rated lower

than A.C.S. side- 66

Technical side lower- 11%

Scale 2

Undetermined ACS Technical

RESULTS-

Additional Results

Deposits due to

additional impurities

Technical grade more

than U.S.P grade

Did not considerably

interfere with fingerprint

quality

Technical ACS

CONCLUSIONS

Little difference in quality of fingerprints developed

Donor error

Lower grade silver nitrate doesn’t impact results of

physical developer

More cost-effective

CONCLUSION

[Fe2+]/[Fe2+]fresh

0.0 0.1 0.80.70.60.50.40.30.2 1.00.9

0.8

0.9

0.7

0.6

0.5

0.4

0.3

0.2

0.1

Good Quality Marks

Development Time ≤ 20 min

Poor Quality Marks

Development Time ≥ 20 min

No Marks Developed

1.0

[Ag

+] /

[Ag

+] f

resh

VALIDATION OF MODIFIED WETWOP

TO DEVELOP FINGERPRINTS ON

TYVEK

INTRODUCTION

Tyvek

Polyethylene fibers

Heat and pressure

Semi-porous Breathable

Water resistant

Tear resistant

Used in envelopes

Wetwop

Powder suspension

Fingerprints on adhesive side of tape

Modified- 25mL Wetwop, 100mL RO-DI water, 10g black powder

SAMPLES

Depletion series

Tyvek envelopes Fed Ex and USPS

Eccrine and Sebaceous

Aged 2 weeks 5 donors- 3 male, 2 female

Aged 2 years 4 donors- 2 male, 2 female

50 strips per test

Pseudo-casework

Fed Ex and USPS envelopes naturally handled

Aged 2 weeks and 2 years

25 envelopes cut into four equal pieces

COMPARISON

Depletion series

Scale

+2 Wetwop much better

+1 Wetwop slightly better

0 Wetwop and other method equal

-1 Other method slightly better

-2 Other method much better

Average ratings

Pseudo-casework

Count number of identifiable fingerprints

Compare totals

TRADITIONAL METHODS

Depletion Series

Aged 2 years

Cyanoacrylate fuming, then cut

Compared cyanoacrylate fuming then black powder

to cyanoacrylate fuming then magnetic powder

Cyanoacrylate fuming then magnetic superior

Compared cyanoacrylate fuming then magnetic

powder to cyanoacrylate fuming then dye stain

(Rhodamine 6G)

Cyanoacrylate fuming then magnetic powder superior

MODIFIED WETWOP METHOD

Compare Wetwop to cyanoacrylate fuming then

magnetic powder

Depletion series and pseudo-casework

Aged 2 weeks and 2 years

Dip samples in modified Wetwop

20 seconds

Rinse

Hang to dry

Blot remaining water

MODIFIED WETOP RESULTS

Depletion Series

Aged two weeks

Average rating- +0.48

Aged two years

Average rating- +0.02

Pseudo-casework

Aged two weeks

Number of identifiable fingerprints using modified wetop- 8

Number of identifiable fingerprints using cyanoacrylate fuming

then magnetic powder- 1

Aged two years

undetermined

Wetwop Magnetic

PSEUDO-CASEWORK RESULTS

Cyanoacrylate fuming then magnetic

powder

Wetwop

CONCLUSION

Modified Wetwop is superior

As fingerprints age, Wetwop’s advantage

diminishes

Further studies

Aging of fingerprints

Padded Pak envelopes

ANY QUESTIONS?