Forensics Journal - Stevenson University 2011 | Page 21

FORENSICS JOURNAL

Eight plates spotted with the twenty-five black inks and eight plates
spotted with the twenty-five blue inks were setup according to the
previously stated methodology. All of the plates were run in solvent
system combination AFG. The plates were photographed and the Rf
values were measured. The average Rf value was calculated for each
ink component visible on the chromatograph. As some ink components were not visible on individual plates, the number of Rf values
for each component ranged from 2-8. The standard deviation was
then calculated for each Rf value; the 95% interval was then calculated using the average +/- two standard deviations.

TABLE 5: GRADING OF PLATES
TRIAL

EXAMINER 1

EXAMINER 2

EXAMINER 3

ADG

3

3

2

BDG

3

3

3

CDG

2

2

2

AEG

3

3

3

BEG

3

2

3

CEG

1

2

1

AFG

3

3

3

BFG

3

2

2

CFG

1

2

1

ADH

1

1

The previously run 24 solvent systems were then viewed to determine
any Rf values inconsistent with the 95% range. The number of inconsistencies above and below the 95% interval of the average Rf value
were tallied and appear in Table 6. If no inconsistencies were present,
the space was left blank. The total number of inconsistencies was
determined for each solvent system. The eighth blue ballpoint ink was
not included in the remainder analyses because a mis-labeling error
was found for the classification number I-2554. No comparisons were
completed on those inks that were labeled as “not visible” when viewing each plate. The number of outliers ranged from a minimum of
9 to a maximum of 184. However, the chosen solvent system, AFG,
contained 23 outliers. Uncontrollable factors such as different plates
and the humidity could have affected the Rf values.

1

BDH

1

1

1

CDH

2

3

2

AEH

2

2

2

BEH

2

2

2

CEH

2

1

2

AFH

1

1

1

BFH

2

2

1

CFH

1

2

1

AIH

2

3

3

BIH

2

2

1

CIH

2

2

1

AIG

1

2

1

BIG

1

2

1

CIG

1

2

1

19