Arielle Cruz
Black inks are usually a mixture of various coloured pigments. Chromatography is a technique that uses capillary action to separate different types of ink at different rates, revealing the colours that were mixed to make the black ink. Paper chromatography is a simple method that can be used to analyse the ink components in black markers/pens. The process involves spotting the ink onto strips of chromatography paper and putting them in a beaker containing a solution of alcohol and water. The water carries some parts of the ink components further than others, and the colours separate out into a range of colours.
| Characteristics | Values |
|---|---|
| Technique used to separate black ink into different colors | Paper Chromatography |
| What is paper chromatography? | A technique that uses capillary action to separate different types of ink at different rates |
| What is capillary action? | A phenomenon where water travels up the paper and when it comes in contact with dried ink pigments, they dissolve and get carried along with the water |
| What is the stationary phase in this process? | The paper or more precisely the water that is adsorbed to the paper molecules |
| What is the mobile phase? | The solvent (alcohol and water solution) |
| What is the solvent attracted to? | The water embedded in the paper (adhesion force) and the solvent to itself (cohesion force) |
| What is the result? | A different component will move a different distance depending on the strength of attraction to each of these objects |
| What is the name chromatography derived from? | The Greek words chroma and graph for “color writing” |
| Who developed chromatography? | Russian botanist Mikhail Tsvet in 1901 |
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Paper chromatography
To perform paper chromatography, you will need chromatography strips or paper, a beaker or jar, isopropyl alcohol or a mixture of solvents, and black markers or pens. Safety goggles, gloves, and adult supervision are recommended when working with isopropyl alcohol.
Begin by placing a flat coffee filter or chromatography paper on a flat surface. Using a black marker or pen, create a solid circle or dot in the centre, and label the paper with the brand of the marker or pen. Then, fill the beaker or jar with a solution of alcohol and water, ensuring that the chromatography strips only touch the surface of the solvent. Alternatively, you can hang the strips so that their tips just touch the solvent.
As the solvent moves up the paper by capillary action, you will observe the black ink separating into different colours. The different pigments in the ink are attracted to the paper and solvent differently, causing them to move at various rates. This process can also be observed by drawing a line with a water-based marker on a coffee filter or paper towel strip and then placing it in fresh water.
After performing the experiment, you can calculate the average Rf (retention factor) for each dye component in the ink by using multiple strips for each pen or marker. Create a data table to record the separated components from each marker or pen. You can also make a bar graph showing the Rf values, with the x-axis representing the different colour components and the y-axis representing the corresponding Rf values.
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Capillary action
In the coffee filter experiment, the water or alcohol moves up the filter paper due to capillary action. The fibres in the paper are packed closely together, allowing the liquid to flow up through capillary action, similar to how liquid moves up the bristles of a paintbrush. As the liquid moves up, it carries the ink particles with it.
The separation of colours in the ink occurs due to the different sizes and densities of the dye molecules. Larger molecules move more slowly and not as far, while smaller molecules move more quickly and farther. This difference in molecule sizes and densities causes the colours to separate into different bands along the filter paper.
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Solvents
The solvent used in paper chromatography is typically a mixture of alcohol and water. The chromatography paper, marked with black ink, is placed in a beaker containing this solution. The solvent moves up the paper through capillary action, a process by which liquid flows in narrow spaces, against gravity. This movement occurs because the attraction of the solvent molecules to the water molecules embedded in the paper (adhesion force) is stronger than the attraction of the solvent molecules to each other (cohesion force).
As the solvent moves up the paper, it interacts with the ink in different ways. The various pigment components of the black ink have different affinities for the solvent, the water in the paper, and each other. This results in the pigments being carried to different heights on the paper, leading to the separation of colours. The pigments with stronger attractions to the solvent will move further, while those with stronger attractions to the water in the paper or to each other will move less or remain stationary.
Different solvents can be used in paper chromatography, including isopropyl alcohol (rubbing alcohol), vinegar, nail polish remover, and turpentine. The choice of solvent can influence the separation of ink colours. For example, when using Jacquard Piñata inks, which are ethanol-based, isopropyl alcohol can reduce the solubility of the dyes, especially with darker colours, causing the dyes to separate into flecks. Additionally, the quality and brand of the ink can impact the separation of colours.
The process of paper chromatography allows us to observe the hidden colours within black ink. By using different solvents and inks, we can explore the interactions between the solvent, ink, and paper, gaining insights into the complex chemistry of colour separation.
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Pigments
Black ink is usually a mixture of various coloured pigments combined with different liquids. Paper chromatography is a technique used to separate these mixtures. In this process, the water moves across the paper by capillary action, carrying some parts of the ink components further than others, and the colours separate into a range of colours. The rate at which each pigment travels depends on the size of the molecule and its attraction to the paper. Since the water carries different pigments at different rates, the black ink separates to reveal the colours that were mixed to make it.
The process of paper chromatography involves spotting chromatography paper with ink and placing it in a beaker containing a solution of alcohol and water. The paper acts as the stationary phase, and the alcohol and water solution is the solvent (mobile phase). The solvent moves by capillary action, and its attraction to the water in the paper is greater than its self-attraction, causing it to move up the paper. The ink is attracted to the water in the paper, itself, and the solvent to varying degrees, causing the different components to move at different speeds and distances.
Different brands of black markers use different combinations of ink to produce their black colour, so each brand separates into its own colour pattern. Certain "permanent" inks use coloured inks dissolved in a different solvent, like alcohol. These inks may not separate into colours.
The technique of chromatography was developed in 1901 by Russian botanist Mikhail Tsvet, who used it to separate the pigments that made up plant dyes.
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Permanent vs water-based inks
Black inks are usually a mixture of various coloured ink pigments in liquid solvents. Paper chromatography is a technique used to separate these mixtures. In this process, the water moves across the paper by capillary action, carrying some parts of the ink components further than others, and the colours separate out into a range of colours.
Permanent inks use coloured inks dissolved in a different solvent, such as alcohol. Water-based inks, on the other hand, utilise water as the main solvent. However, this does not mean that water is the only solvent used. Many water-based inks contain "co-solvents", which may even be petroleum-based. These co-solvents are used to decrease the time and heat necessary to cure the ink film on the fabric. Water-based inks are a good choice when a "soft hand" is desirable, meaning that the ink film cannot easily be felt when passed across the fabric. They are also a good choice when ink penetration is desirable, such as in towel printing.
Water-based inks can be air-dried, but they are usually only acceptable for craft-level printing as the room required for curing greatly reduces productivity. They can also be cured more quickly with the addition of a catalyst, which will continue the curing process even if all the water is not removed. However, once a catalyst is added, it creates a time limit, or "pot life", after which the ink must be discarded. Water-based inks are also more likely to dry in the screen, which can be a problem if the screen is left between prints.
In comparison, permanent inks are more likely to be resistant to water, whereas water-based inks will run even after completely drying.
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Frequently asked questions
Black inks are usually a mixture of a variety of colored pigments. Chromatography is a technique used to separate mixtures. The alcohol acts as a solvent, and the different pigments are carried along at different rates, causing them to separate and revealing the colors that were mixed to make the black ink.
Chromatography is a technique that uses capillary action to separate different types of ink at different rates. The name comes from the Greek words "chroma" and "graph", meaning "color writing".
In chromatography, a gas or liquid flows through a stationary substance. In the case of black ink and alcohol, the ink is spotted onto strips of chromatography paper and put in a beaker containing an alcohol and water solution. The water in the solution travels up the paper due to capillary action and carries the different pigments at different rates, causing them to separate.
Other solvents that can be used in chromatography include rubbing alcohol, vinegar, nail polish remover, and turpentine.
