Fiber Guidelines, Appendix B of Chapter 4 (FSC, April 1999)
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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.