Painting on Paper

Here's how the extracted natural dye looks on a piece of drawing paper:
(Notice that the colour darkens when it has dried.)

Putting in into a picture:

Extracting not so Water-Soluble Pigments

Not all pigments from plants are water-soluble. Thus, they would have to be extracted using organic solvents.

CARROTS contain beta-carotene, which is the compound that gives it the orange colour.  This compound is very non-polar and would not dissolve in water (polar molecule), but instead it would dissolve in non-polar organic solvent, such as hexane.

Structure of beta-carotene molecule

Using hexane to extract yellow pigment from carrot

Yellow / orange pigment can also be extracted from TUMERIC.  This pigment arises from curcumin, which is a much more polar molecule as compared to beta-carotene.  However, it is more soluble in ethanol than in water, thus making ethanol a more suitable solvent to extract the pigment.

Structure of curcumin molecule

Footnote:

• Commonly used organic solvents:  ethanol, acetone, ethyl acetate, hexane...
• It is extremely important to check the health / environmental hazards of the organic solvents before using them!  This information can be found in the Material Safety Data Sheet (MSDS) that is available in many websites.
• Organic solvents must NOT be disposed into the sink!

Extracting Water-Soluble Dye from Vegetables & Fruits

RED CABBAGE contains a water-soluble pigment that is purple at neutral pH.  This colouring can be easily extracted from the vegetable by boiling it in water.

The resultant extracted colouring is decanted and/or filtered to remove the cabbage pieces. This purple pigment changes to red when in an acidic solution, and changes to green when in an alkaline (basic) solution.

 
BEET ROOT also contains water-soluble pigment, which can be obtained by removing the skin, cutting it into small pieces and boiling them in water.

Blue pigment can be extracted from the SKIN of BLUEBERRIES by boiling it in water.  If the whole fruit is boiled in water, you end up with jam!  As the fruit is boiled, it softens and sugar from the fresh of the fruit would also dissolve into water. This results in a sweet-smelling, thick mixture (see picture below) that is very difficult to filter.

Footnote:  

• If you feel that the colour is too diluted when you paint it on paper / cloth, you might want to boil off some water to make the colour darker.  However, the colour of the solution might change if it is heated for too long.
• Looking around you for more colourful vegetables, fruits or even flowers and other parts of a plant!
• Read more about the anthocyanins, which is the group of compounds that are responsible for the colourings.

Blue Dye from Butterfly Pea Flower

A blue dye is commonly extracted from the flowers of Butterfly Pea (Clitoria ternatea), to colour nonya cakes.

At home, the colour can be extracted by pouring hot water on the flowers.  However, in the lab, we have the option of using various solvents.

Using acetone and ethanol, which are common organic solvents, the blue dye can be extracted by soaking the flowers in them.  It is observed that the tone of the extract in acetone is slightly different from that of ethanol and water.  This could be due to the extraction of the non-polar pigment(s) from the flower, since acetone is a less polar solvent as compared to ethanol and water.  The advantage of using acetone or ethanol (as compared to water) is that the solution can be concentrated using the rotary evaporator, since these organic solvents have lower boiling points.  As the solution become more concentrated, so will the intensity of the colour of the dye.

It is worth noting that the acetone extract decolourises after a couple of days.  Also, if the flowers had been kept (in a refrigerator) for a few weeks, the extract would appear more greenish.  It is important that the flowers should be kept in the refrigerator, in a ziplop bag, to prevent it from drying up.

Extraction can be done more efficiently by grinding the petals gently in a mortar and pestle. However, in doing this, would produce small solid particles, which can be simply removed by filtration. One trick in doing a simple filtration quickly, is to use a small ball of cotton instead of a filter paper.

The dye has appeared to be stable in ethanol after storing it for a few weeks. Thus, this solution can be kept until it is ready for use.

Extracting Pigments from Spinach

The leaves of green vegetables contain chlorophyll, which can be extracted using the following method.


Materials Required

• Spinach leaves
• Mortar & pestle
• Pasteur pipette (dropper)
• Test-tube
• Acetone
• Hexane

Procedures

1. Tear the spinach leaves into small pieces and place them in a mortar.
2. Add approximately 10 mL of acetone and carefully grind the sample and acetone together with the pestle. Continue grinding until the acetone becomes dark in colour. More acetone may be added to compensate for evaporation.
3. Using a disposable Pasteur pipette, extract the acetone and place it in a small test tube. Be careful not to extract the small pieces of vegetable.
4. Repeat steps 2 and 3 using the same vegetable remaining in the mortar, until the test tube is approximately 1/3 full.
5. Add approximately 3 mL of hexane to the acetone extract.
6. Mix the contents of the test tube by using a clean disposable Pasteur pipet to repeatedly withdraw a sample and then immediately dispensing the sample back into the test tube. Be careful not to let the test tube overflow.
7. Let the mixture stand to allow the two layers to separate.
8. Draw out the upper hexane layer from the test tube.

This dark green extract can be separated on Thin Layer Chromatography:

See a video demonstration by Peter Keusch (scroll down the page to the end of "experimental procedure").

Online Resources

Here are some websites to help you explore natural dyeing:

• About.com Chemistry: Home and Garden pH Indicators 
• About.com Chemistry: Red Cabbage pH Indicator
• Aurora Silk's How to Use Natural Dyes
• Autonopedia: Making Natural Dyes from Plants
• DIY: Make Natural Non Toxic Dye
• Natural Easter Egg Dyes
• Pioneer Thinking - Natural Dye Crafts
• Vicki Cobb's Red-Cabbage Indicator
• White Dragon's Using Natural Plant Dyes

History of Natural Dyes

Since ancient times, man had used colours from various parts of the plants, insects, minerals and even marine organisms to dye their textiles.

Take a trip back in time and discover the rich history of natural dyes:

• Dye History by Susan C. Druding
• Quilt History
• Wikipedia - Dye