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forensic chem > chemistry of color /colorants (ch..14) > Flashcards

chemistry of color /colorants (ch..14) Flashcards

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1
Q

what are colorants?

A

in Forensic interest… are in dyes and pigments and are applied to fibers,inks,paint

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2
Q

where does color arise ?

A

chemical structure; conjugated systems

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3
Q

T/F it is hard to quantitate color

A

T

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4
Q

humans can sense EM radiation from____

A

380-700nm

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5
Q

response to receptor cells in the ___

A

retina

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6
Q

the __ are responsible for night and peripheral vision

A

rods

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7
Q

__ provide color sensing

A

cones

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8
Q

what are the 3 types of cones ?

A

red,green, and blue (RBG)

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9
Q

how does the CIE system express findings?

A

using X and Y derived from a reflective spectrum that is a combination of the primary spectrum

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10
Q

what is the goal of CIE ?

A

to express color as a weighted average of RGB and convert to be plotted in 2 dimensions

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11
Q

what is the Munsell system ?

A

(Albert Munsell)
- similar to CIE
uses the three variables : hue,brightness, and saturation

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12
Q

Munsell charts are used in forensic analysis of ___ and ___

A

paints and soils

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13
Q

CMY system (____) is used for ___

A

cyan-magenta-yellow
printers

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14
Q

RGB (____) is used for ___

A

red-green-blue
monitors

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15
Q

when do we use colorants ?

A

analytical chemistry : use of dyes as acid/base indicators
histological stains: used in the biological disciplines are dyes

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16
Q

what is the difference between pigments and dyes ?

A

** dyes will penetrate a paper with solvent, pigments in paint dry on top**
- solubility ; dyes are soluble in solvent they are carried
- dye has an affinity for their substrate, pigments do not

17
Q

T/F pigments are suspended particulates

A

true

18
Q

T/F pigments are nonmetallic

A

F: they are metallic and contain a transition metal , some are organic

19
Q

Ink consists of __

A

solvent, colorants(dyes/pigments/both), and other additives (to control thickness and appearance when dried)

20
Q

what inks are used for ink formulations ?

A

methyl , methyl ketones, isophorone, and glycol ethers

21
Q

different types of inks:

A

printing ink, ballpoint pen ink, gel pen inks, typing ribbons

22
Q

___ used to stabilize the double layer of pigments

A

surfactants

23
Q

what resins control the viscosity ?

A

adhesives

24
Q

what is the oldest ink?

A

carbon ink (India ink)

25
Q

what is the dot matrix printer?

A

like a typewriter, uses an impact method to create letters by striking paper through an inked ribbon (series of dots)

26
Q

which printers are non - impact ?

A

laser printers, photocopiers, and ink-jet printers
laser: rotation drum surface , scanning the grid
ink: similar to dot except the ink is sprayed

27
Q

what is toner

A

toner is a dry powdery material that contains waxy plastic and colorant

28
Q

toner cartridges include :

A

black, yellow, magenta, and cyan (CMY)

29
Q

what does a toner do?

A

(-) charged toner applied to the drum and adheres, paper with a charge is rolled on the drum –> transferring toner from drum to paper (by heat which melts the waxy toner)

30
Q

what is the purpose of mechanical printing?

A

we use this for dollar bills (which is hard to recreate through counterfeiters)

31
Q

process of mechanical printing?

A
  • cast of the dye made of plastic (alto)
  • placed in electrolyte solution
  • plate is coated with ink
  • special paper is rolled across the plate to transfer the ink on the surface ; acquiring ridges and grooves
32
Q

ancient paints used ___ as binding agents

A

beeswax and fats

32
Q

what are the 3 elements of paints

A

solvent (organic or water)which evaporates, a colorants (pigment), and binding agent that polymerizes during curing stage

32
Q

T/F paints can be cured unassisted

A

T ; or even by UV/heat

33
Q

paint on a porous or nonporous system use a layer system: what is that process?

A
  • a primer Is added (prepare the substrate)
  • the colorants layer is added (dye/pigment)
  • protective layer of varnish or clear coat
34
Q

latex paints are water based but have challenges since__

A

binders and resins are not soluble but used as micelles; surround and dissolve monomers (which polymerizes)

35
Q

once the latex paint is applied to the substrate …

A

the water evaporates and allows the polymerization to proceed to completion

36
Q

T/F cars are painted in a complex layering system

A

T: can be used to differentiation 2 systems

37
Q

** know 3 layer method she has on page 6 **

A

and do study guide !!!!!!!

forensic chem (5 decks)

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