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April 1999 Volume 1
Number 1
Chapter 4 of Forensic Fiber
Examination Guidelines
Appendix B:
Classification of Dyes
WOOL Fibers (17)
Stage 1
Pyridine/Water
(4:3), 100°C, 10 minutes
Good extraction »
ACID dye
Little or no extraction—Go to Stage 2
Stage 2
2% aqueous oxalic
acid, 100°C, 20 minutes then pyridine/water (4:3), 100°C, 10 minutes
Improved extraction »
METALIZED Dye
Little or no extraction »
REACTIVE Dye
COTTON and VISCOSE Fibers
(15)
Stage 1
Glacial acetic
acid, 100°C, 20 minutes
Good extraction »
AZOIC Dye
Little or no extraction
Go to Stage 2
Stage 2
Pyridine/Water
(4:3), 100°C, 20 minutes
Good extraction »
DIRECT Dye
Little or no extraction
Go to Stage 3
Stage 3
Dithionite/polyvinylpyrrolidone,
(see endnote 1 of this appendix) 100°C, 20
minutes (see endnote 1)
Apply extract to TLC plate; check color of spot
Fiber color changed »
REACTIVE Dye
(No colored spot or spot not original fiber color)
Fiber color unchanged »
INGRAIN Dye
(No colored spot or spot not original fiber color)
Fiber color changed
Go to Stage 4
(original colored spot)
Stage 4
10-14% Sodium
hydroxide, 100°C, 10 minutes (new fiber)
Fiber color changed
» SULFUR Dye
Fiber color unchanged »
VAT Dye
ACRYLIC Fibers (13)
Stage 1
Formic acid/water
(1:1), 100°C, 20 minutes
Good extraction—Go to Stage 2
Stage 2
TLC procedure—methyl
acetate eluent
Movement » DISPERSE Dye
No movement—Go to Stage 3
Stage 3
TLC procedure—methanol
eluent
Sharp line at solvent front »
ACID Dye
Little or no movement or smearing »
BASIC Dye
POLYESTER Fibers (7)
Stage 1
Chlorobenzene,
130°C, 10 minutes
Good extraction »
DISPERSE Dye
Little or no extraction—Go to Stage 2
Stage 2
Dimethylformamide/formic
acid (1:1), 100°C, 20 minutes
Good extraction »
BASIC Dye.
POLYAMIDE Fibers (7)
Stage 1
Chlorobenzene,
150°C, 15 minutes
Little or no extraction—Go to Stage 2
Good extraction »
DISPERSE Dye
Stage 2
Pyridine/water
(4:3), 100°C, 20 minutes
Little or no extraction »
REACTIVE or DIAZO Dye
Good extraction—Go to Stage 3
Stage 3
TLC procedure—methanol
eluent
Sharp line at solvent front »
ACID Dye
Little or no movement or smearing »
BASIC Dye
POLYPROPYLENE Fibers (11)
Stage 1
Methyl acetate/water/acetic
acid (5:5:1), 100°C, 20 minutes
Good extraction »
DISPERSE Dye
Little or no extraction—Go to Stage 2
Stage 2
Pyridine/ water
(4:3), 100°C, 20 minutes
No extraction » PIGMENT
Some extraction—Go to Stage 3
Stage 3
2% aqueous oxalic
acid, 100°C, 20 minutes then Pyridine/water (4:3), 100°C,
20 minutes
Improved extraction »
METALLIC Dye
No improvement » ACID Dye
ACETATE/TRIACETATE Fibers
(9)
Stage 1
CA pyridine/water
(4:3), room temperature, 15 minutes
CTA pyridine/water (4:3), 100°C, 20 minutes
Little or no extraction
= DIAZO Dye
Good extraction = DISPERSE Dye
Endnote
1. Dithionite/polyvinlypyrrolidone—Use
immediately and discard excess:
80 mg sodium dithionite
30 mg polyvinylpyrrolidone
450 mL 10% sodium hydroxide
9 mL water.
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FORENSIC SCIENCE COMMUNICATIONS APRIL 1999 VOLUME 1 NUMBER 1 |
