chemistry of color /colorants (ch..14) Flashcards
what are colorants?
in Forensic interest… are in dyes and pigments and are applied to fibers,inks,paint
where does color arise ?
chemical structure; conjugated systems
T/F it is hard to quantitate color
T
humans can sense EM radiation from____
380-700nm
response to receptor cells in the ___
retina
the __ are responsible for night and peripheral vision
rods
__ provide color sensing
cones
what are the 3 types of cones ?
red,green, and blue (RBG)
how does the CIE system express findings?
using X and Y derived from a reflective spectrum that is a combination of the primary spectrum
what is the goal of CIE ?
to express color as a weighted average of RGB and convert to be plotted in 2 dimensions
what is the Munsell system ?
(Albert Munsell)
- similar to CIE
uses the three variables : hue,brightness, and saturation
Munsell charts are used in forensic analysis of ___ and ___
paints and soils
CMY system (____) is used for ___
cyan-magenta-yellow
printers
RGB (____) is used for ___
red-green-blue
monitors
when do we use colorants ?
analytical chemistry : use of dyes as acid/base indicators
histological stains: used in the biological disciplines are dyes
what is the difference between pigments and dyes ?
** 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
T/F pigments are suspended particulates
true
T/F pigments are nonmetallic
F: they are metallic and contain a transition metal , some are organic
Ink consists of __
solvent, colorants(dyes/pigments/both), and other additives (to control thickness and appearance when dried)
what inks are used for ink formulations ?
methyl , methyl ketones, isophorone, and glycol ethers
different types of inks:
printing ink, ballpoint pen ink, gel pen inks, typing ribbons
___ used to stabilize the double layer of pigments
surfactants
what resins control the viscosity ?
adhesives
what is the oldest ink?
carbon ink (India ink)
what is the dot matrix printer?
like a typewriter, uses an impact method to create letters by striking paper through an inked ribbon (series of dots)
which printers are non - impact ?
laser printers, photocopiers, and ink-jet printers
laser: rotation drum surface , scanning the grid
ink: similar to dot except the ink is sprayed
what is toner
toner is a dry powdery material that contains waxy plastic and colorant
toner cartridges include :
black, yellow, magenta, and cyan (CMY)
what does a toner do?
(-) 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)
what is the purpose of mechanical printing?
we use this for dollar bills (which is hard to recreate through counterfeiters)
process of mechanical printing?
- 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
ancient paints used ___ as binding agents
beeswax and fats
what are the 3 elements of paints
solvent (organic or water)which evaporates, a colorants (pigment), and binding agent that polymerizes during curing stage
T/F paints can be cured unassisted
T ; or even by UV/heat
paint on a porous or nonporous system use a layer system: what is that process?
- a primer Is added (prepare the substrate)
- the colorants layer is added (dye/pigment)
- protective layer of varnish or clear coat
latex paints are water based but have challenges since__
binders and resins are not soluble but used as micelles; surround and dissolve monomers (which polymerizes)
once the latex paint is applied to the substrate …
the water evaporates and allows the polymerization to proceed to completion
T/F cars are painted in a complex layering system
T: can be used to differentiation 2 systems
** know 3 layer method she has on page 6 **
and do study guide !!!!!!!
