4103FSBMOL - Lecture 5 - Chemistry of Colour. Flashcards
Systems used in Forensic Science to describe and quantify colour, Dyes and Pigments, Inks and Paint and Forensic Techniques used to analyse dyes in inks and fibres and pigments in paints.
What are the 2 different Systems used to describe/ quantify colour?
- The CIE System.
- The Munsell System.
Colour is ____________.
Subjective.
Why is colour subjective?
Because different people would identify a colour differently (based of opinions).
What part of the electromagnetic spectrum does sunlight contain?
(that we care about for the Chemistry of Colour)
Visible Light Spectrum.
What range is the Visible Light part of the Electromagnetic Spectrum?
400-700nm.
The colour white is seen as white, as it __________ all colours of visible light.
Reflects.
The colour black is seen as black, as it __________ all colours of visible light.
Absorbs.
What part of our eye are the 3 Coloured Cones?
In our Retinas.
What are the 3 different coloured cones in our retinas?
Blue, Green and Red.
What colour cone is stimulated by the Red colour?
The Red Cone.
What colour cone is stimulated by the Blue colour?
The Blue Cone.
What colour cone is stimulated by the Green colour?
The Green Cone.
What colour cones are stipulated by a white colour?
(what percentages of each)
All 3 cones (Blue, Green and Red) equally - 33% each.
A mixed colour such as Orange is stipulated by what cones?
The Red and Green cones (more of the red cone).
What does a mixed colour such as Yellow mean compared to the mixed colour Orange?
The Green Cone is being stipulated more then the Red Cone.
When was the CIE colour system first published?
1931.
What does the CIE System characterise colour based off?
The Blue, Green and Red coloured cones in our retinas. It uses mathematical numbers and tristimulus values.
What are Tristimulus Values?
Tristimulus values are percentages of the components in a three-colour additive mixture necessary to match a colour in the CIE system.
What are the Tristimulus values designated in the CIE Colour System?
X, Y and Z.
Which Tristimulus Value does the Red colour relate to?
Z.
Which Tristimulus Value does the Blue colour relate to?
X.
Which Tristimulus Value does the Green colour relate to?
Y.
What do Tristimulus values always have to be?
Positive.
What colour do equal values of X, Y and Z produce in the CIE system?
White.
Which Tristimulus value controls the luminescence (brigtness) of colour?
The Y-coordinate colour.
What is the Name of the Diagram which the CIE system is based off?
Chromaticity Diagram.
How are the X, Y, Z Tristimulus Values converted into the 2 - x and y values for the Chromaticity Diagram?
(Don’t think it’s neccessary to know).
The Reflectance (Rλ) and Weighting Function values for each of the X, Y and Z peaks (WX, WY, WZ) *are multipled together.** The x-coordinate can be calculated from: x = X / X+Y+Z and the y-coordinate from y = Y / X+Y+Z.
Rλ multiplied WX = X, Rλ multiplied WY = Y, Rλ multiplied WZ = Z.
What shape is the Chromaticity Diagram?
A Hyper-parabola Shape.
What colour has the largest representation on the Chromaticity Diagram?
Green.
Can the CIE System describe or quantify colour? Why?
It can only describe colour as not all colours are equally proportionated on the Chromaticity Diagram.
What is the Munsell System used for?
To quantify the colour of soil.
What 3 parts is the Munsell System Split into?
- Hue.
- Value.
- Chroma.
What is the Hue in the Munsell System?
It is the base colour we see which is split into 5 basic colours by Munsell.
What are the 5 basic colours by Munsell?
Red, Yellow, Green, Blue and Purple.
What shape is the Hue in the Munsell System Diagram?
Wrapped into a circle around the main central pole.
What is the Value in the Munsell System?
The Tonal Value is used to describe how light or dark a colour is (vertical axis) going from Black (0) to White (10).
What shape is the Value in the Munsell System Diagram?
The Main Central Pole of the Diagram.
What is the Chroma in the Munsell System?
It describes the purity/ intensity/ strength of the colour. Chroma is split into 10 steps away from the centre pole.
What does a Higher Chroma number mean?
Stronger the Strength of the colour.
What does a Lower Chroma number mean?
Weaker the Strength of the colour.
What shape is the Chroma in the Munsell System Diagram?
Bands ranging from the central pole (Value) to the outer ring of Hue.
Weaker colour bands towards the centre, stronger bands towards the outside.
As purple is a Strong (Main) colour, what does it mean for the Chroma value compared to weaker colours?
The Chroma value can be higher (reaches 26 in purple, compared to only 10 in an orange colour).
How do you work out the Exact Colour (Unique Identifier Code) using the Munsell Colour System?
The first part is from the Hue (e.g. 5P is strong purple) then the next part is in the form Value/ Chroma. The strongest colour of Purple is classified as 5/26 as the Value 5 is central and the Chroma is at its maximum of 26.
(5P 5/26 - Strongest Purple Colour).
What is an issue when trying to quantify the colour of soil?
Soil is a different colour in Wet and Dry Conditions.
Practice Question:
Which Colour system can only be used to describe colour?
- CIE System.
- Munsell System.
- CIE System.
Practice Question:
In the Munsell System which variable is described as the purity of the colour?
- Hue.
- Value.
- Chroma.
- Chroma.
Practice Question:
In the Munsell System which variable is described as the actual colour?
- Hue.
- Value.
- Chroma.
- Hue.
Practice Question:
In the Munsell System which variable is described as the tone/ brightness?
- Hue.
- Value.
- Chroma.
- Value.
What is another name for a Colourant and what do they do?
Chromaphore - they impart the colour to an object.
What are Colourants a formulation of?
Pigments or Dyes and additives.
What is a Dye?
They are soluble in the solvent they are contained in - affinity for the substrate they are deposited on. They penetrate into the substrate.
What is a Pigment?
Give an example.
They are particles suspended in a solvent. They have no affinity for the substrate. Pigements for a layer on top of the substrate and don’t penetrate into the substrate.
An example is gloss paint on top of a piece of paper.
What are the 5 main types of Dye?
- Acid.
- Basic.
- Azo.
- Natural.
- Direct.
What are Acid Dyes used for?
The detection of Bloody Fingerprints.
What are Basic Dyes used for?
Detection of grease contaminated fingerprints.
What are Azo Dyes?
They are the produce of the Fast Blue BB Salt test. They are used in the Textiles Industry.
What are Direct Dyes used for?
They are used in the Textiles Industry to dye clothes.
What are the 3 main types of Pigment?
- Inorganic.
- Organometallic.
- Natural.
What is an example of an Inorganic Pigment?
Titanium Dioxide - found in white paint.
What is an example of an Organometallic Pigment?
Transition metal surrounded by organic molecules (e.g. copper thylacynite - pigment in paint, used in inks and the development of fingerprints).
What is an example of a Natural Pigment?
Red/ Yellow Ochre can be found in the Earth’s Crust. Lapis Lazuli, Murex Purple is the most expensive pigment.
How do you get the Murex Purple Pigment and how much does it cost?
It is extracted from the mediterranean sea snail and costs £500,000 for 28 grammes.
What do pigments produce in terms of light?
They produce the scattering of light - greater the scattering, the greater the opacity of paint.
What is the definition of Opacity?
The ability of paint to stop the transmission of light.
What is the difference between how many coats of paint are needed for certain opacities?
High opacity paint only needs 1 application, low opacity paints require multiple coats. Low opacity paints won’t stop the transmission of a previous colour base paint (light).
How do you optimise the scattering of pigment particles?
You have to ensure the diameter of the pigment particles are half that of the incident light wavelengths.
White Paint has a diameter of 200-400nm (half of 400-800nm visible light).
What can paint be described as?
A liquid that oxidises in the air OR a coloured powder in a glue like medium.
What are the 5 things that Paint is composed of?
- Water.
- Pigment.
- Binder.
- Surfactant and Antifoam.
- Thickener.
What is the Pigment used for in Paint?
To give the colour and opacity of the paint.
What is the Binder used for in Paint?
To bind the pigment to the wall.
What is the Surfactant and Antifoam used for in Paint?
To reduce/ remove the bubbles in your paint.
What is the Thickener used for in Paint?
To thicken the paint on the wall so it dries.
The Pigment in paint must have a __________ refractive index (RI) than the binder.
Higher/ Lower?
Higher.
To recap, what ways are there to Maximise the Scattering, Reflection and Opacity of the Paint?
- Pigment Strength.
- Size of Particles must be half that of incident light.
- RI of Pigment > Ri of Binder.
What Type of Pigment is Titanium Dioxide (TiO2)?
An Inorganic Pigment.
How many different Crystal Structures does TiO2 exist in?
Three.
Name the Crystal Structures of TiO2.
- Rutile.
- Anatase.
- Brooktite.
Out of TiO2’s crystal structures which is/are the only one(s) to be used in white paint production?
ONLY Rutile and Anatase.
Why is Rutile used in White Paint?
Because it has the Best Opacity due to having a higher RI value than Anatase.
(Rutile = 2.7RI and Anatase = 2.55 RI).
Why is Anatase used in White Paint?
It produces whiter paint.
What is special about Paint which contains Titanium Dioxide in it?
(What is the name for the type of Paint).
It is self-cleaning (Photocatalytic Paint) as the sun oxidises any dirt on it and then the rain/ water washes it away.
What are the 3 other types of Pigments?
- Luminescent.
- Pearlescent.
- Thermochromic.
What are Luminescent Pigments?
Give an example.
They are used in florescent inks and paints. They absorb photons of light of a specific wavelength and emit photons of light of a longer wavelength.
They are used in Emergency Exit Signs.
What are Pearlescent Pigments?
Give an example of how they are used.
They give a shimmering effect and are used on cars. Coating of TiO2 (high RI) with a thin layer of mica (low RI). Shimmering occurs from the difference in the RI of the pigment and the mica.
What are Thermochromic Pigments?
Give an example of where they are used.
They change colour when heated up or cooled down. The pigments are sensitive to temperature.
Used in the Mini Chameleon car (changes colour depending on weather and heat).
Practice Question:
________ are particles suspended in a solvent?
- Dyes.
- Pigments.
- Pigments.
Practice Question:
What Pigment is found in white paint?
- Titanium Dioxide.
- Copper Phthalocyanine.
- Titanium Dioxide.
Practice Question:
Which crystal structure of Titanium dioxide produces white paint with the highest opacity?
- Brooktite.
- Anatase.
- Rutile.
- Rutile.
Practice Question:
A pigment that changes colour with temperature is a _______________ pigment
- Luminescent.
- Pearlescent.
- Thermochromic.
- Do not know.
- Thermochromic.
What type of Dye is Solvent Black?
What is it used for Forensically?
An Azo Dye (N=N bond).
Detecting Grease Contaminated Fingerprints.
What type of Dye is Gentian Violet?
What is it used for Forensically?
A Basic Dye.
It is used to identify sebaceous (oil based) fingerprints on the adhesive side of tape.
What type of Dye are Acid Yellow, Black ad Violet?
What are they used for Forensically?
They are Acid Dyes.
They bind to the haem group in blood to enhance bloody fingerprints.
What type of Dye is Indigo?
What is it used for?
It is a Carbonyl Dye found in blue fibres.
It is used to Dye the colour of jeans in the textile industry.
What is Methyl Violet the main Dye for?
What is it used for Forensically?
Ballpoint Pens
It is found in pens so can be used in document forgery detection.
What is Basic Red 40 used for?
It is used in White Superglue Fuming.
What are Copper Phthalocyanines used for?
They are used as pigments in paints.
Practice Question:
What type of dye is Indigo and how is it used in forensic chemistry?
- Acid dye, detect bloody fingerprints.
- Carbonyl dye, found in blue fibres.
- Basic dye, detects sebaceous fingerprints.
- Carbonyl dye, found in blue fibres.
Practice Question:
Acid violet is an acidic dye. What is the forensic use of this dye?
- Detect sebaceous fingerprints.
- Superglue Fuming.
- Detect bloody fingerprints.
- Detect bloody fingerprints.
Practice Question:
From the list below which dye is an Azo dye?
- Indigo.
- Acid Yellow.
- Basic Red 18.
- Solvent Black.
- Solvent Black.
What are the 3 General Components of Inks?
- Colourants.
- Solvents.
- Additives.
What do Colourants do in Inks?
They are the Dyes and Pigments which impart colour to the inks.
What do Solvents do in Inks?
The Dyes are dissolved in/ pigment particles are suspended in the solvents.
What do Additives do in Inks?
They are chemicals used by ink formulators - secret ingredients - which are put in formulations to change the features.
What happens with Fountain Pens to make them go from blue synthetic dyes to black writing?
The blue synthetic dyes initially writes in blue, but then it oxidises to a black colour.
What Dye do ALL Ballpoint Pens have?
Methyl Violet.
What does it mean if the Dye is made of water soluble inks?
They aren’t always permanent.
What type of Dye(s) is/are used in Fountain Pen Inks?
Iron-Gallotanate (Synthetic Dyes).
What type of Dye(s) is/are used in Ballpoint Pen Inks?
Methyl Violet, Victoria Blue, Rhodamine Red, Victoria Green, Copper Phthalocyanine, Azosol, Luxol Fast and Spirit Soluble.
What type of Dye(s) is/are used in Rolling Ball Marker Inks?
Water Soluble or Acidic Dye Salts.
What type of Dye(s) is/are used in Fibre Tip Inks?
Water Soluble or Xylene Based Inks.
What are the Solvents in pens based on?
The age of the Pen - if it was produced before 1952, it will contain a Linseed Oil Based Solvent. After that, they moved to Glycol Based Solvents.
Why is 1952 an important date for Pens?
Because its when Bic made their first Ballpoint pen, so is when the solvent changed from Linseed Based to Glycol Based.
What type of Solvent(s) is/are used in Oil Based Pens?
Mineral Oils, Linseed Oil, Recinoleic Acid and Coconut Fatty Acids.
What type of Solvent(s) is/are used in Glycol Based Pens?
Ethylene glycol, glycerin, benzyl alcohol and ethylene glycol monomethylether.
What type of Pen are most Additives found in?
Ballpoint Ink Pens.
What Additives are found in Ballpoint Ink Pens?
- Fatty Acids.
- Natural Resins/ Synthetic Polymers.
- Surface Active Agents.
- Other organic Additives.
- Defoaming Agent.
What is the role of Fatty Acids as an Additive in Pens?
They are used as a lubricant for the ball in the pen.
What is the role of Natural Resins/ Synthetic Polymers as an Additive in Pens?
They are used to help dissolve your inks within the solvent to make the ink go further (last longer), so it’s cheaper.
What is the role of Surface Acive Agents as an Additive in Pens?
They are molecules with the capacity to adsorb to solid surfaces and/or fluid interfaces.
What is the role of Other organic additives in Pens?
They can help to prevent your ink from corroding.
What is the role of Defoaming Agents as an Additive in Pens?
They can be used in pens to prevent bubbles forming in your ink.
What is the role of Glycols and Formamide’s as Additives in Pens?
They are there to ensure the rolling ball marker or fibre tip pen doesn’t dry out when you leave the lid off.
What is the main use of UV-Visible Spectroscopy for Forensic Analysis of Dyes in Inks?
To be able to help differentiate between inks.
On a UV-Vis Spectrum, what wavelength is the Methyl Violet Peak?
500-600nm.
What type/ types of Spectroscopy do you have to use to confirm the composition of pens?
IR Spectroscopy and/or Raman Spectroscopy.
What piece of equipment can we use to analyse pigments in paint?
ATR-FTIR.
What does using 2 pieces of Spectroscopy Equipment allow you to achieve when analysing inks?
It allow you to analsyse in more detail and compare more accurately.
Which 2 types of Spectroscopy look very similar in the graphs?
IR and Raman Spectroscopy.
When using Raman and FTIR, what does Raman allow you to differentiate in white paint which FTIR doesn’t?
The difference between Anatase and Rutile, whereas FTIR can’t do this.
What does XRF stand for?
X-Ray Fluorescence.
What is XRF?
It is a non-destructive analytical technique that determines the elemental composition of a material by measuring the X-rays it emits.
What is the difference between Dyes and Pigments?
A Dye is soluble in the solvent that it is contained in and has an affinity for the substrate. A Pigment is contained of particles suspended in the solvent and they don’t interact (no affinity) with the substrate.
What are the Main Forensic Techniques to be able to analyse pigments in Paint?
(in detail).
FTIR, Raman and XRF.
What are the different techniques to be able to analyse dyes in fibres?
- ATR-FTIR.
- HPLC and TLC.
- UV-Vis.
How do we use ATR-FTIR to analyse dyes in fibres?
The ATR-FTIR machine usually has a fibre analysing attachment to analyse fibres and the dyes within them.
Is ATR-FTIR destructive or non-destructive?
Non-Destructive.
How do we use HPLC and TLC to analyse dyes in fibres?
The dye has to first be extracted out of the fibre into a solvent and then it can be analysed using a HPLC and/or TLC machine.
Is HPLC and TLC a destructive or non-destructive technique?
Destructive as you have to take the dye out of the fibre.
How do we use UV-Vis to analyse dyes in fibres?
It can either be analysed with or without a microscope attached to the UV-Vis. Without it, you have to extract the dye from the fibre into a solvent, place it into a cuvette and then analyse using UV-Visible Spectroscopy.
Is UV-Visible Spectroscopy a destructive or non-destructive technique?
Non-destructive when its got a microscope attached, otherwise its destructive.
