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Picture of an artistic seal

 

Making Paints

What's it all about?

Many chemicals will not dissolve in water, so when they are made by a chemical reaction they form a cloudy precipitate of undissolved solid. The tricky bit with paints is finding chemicals that will make a coloured precipitate. We use three reactions to make blue, yellow and white paints, which can be painted onto paper or white hardboard. Making the paints is fun and stretches the studentsí practical skills.

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Photo of checking the solid paint

Photo of preparing paints

Photo of preparing paints

Photo of successful painting

 

Student notes

The student notes are divided into four parts, making blue, making yellow, making white, and making the paints.

Making blue

Make Solution 1 by dissolving 2g of iron(II) sulphate in 4cm3 of distilled water. Make Solution 2 by dissolving 1g of potassium hexacyanoferrate(III) in 3cm3 of distilled water.

Make your blue colour by adding Solution 2 to Solution 1 drop-by-drop, swirling the flask thoroughly each time. Go on to making the paints.

Making yellow

Make Solution 1 by dissolving 4g of potassium iodide in 10cm3 of distilled water. Make Solution 2 by dissolving 4g of lead nitrate (care - toxic) in 10cm3 of distilled water.

Make your yellow colour by mixing the two solutions together. Go on to making the paints.

Making white

Make Solution 1 by dissolving 2.5g of sodium chloride in 10cm3 of distilled water. Make Solution 2 by dissolving 6g of lead nitrate (care - toxic) in 10cm3 of distilled water.

Make your white colour by mixing the two solutions together. Go on to making the paints.

Making the paints

First separate the coloured solid from the water by filtration. Set up a Buchner funnel, filter paper and Buchner flask as shown in the diagram. Connect the Buchner flask to the water pump and turn on the water supply. Carefully pour your liquid into the Buchner funnel. The water will be sucked away leaving your coloured solid behind.Diagram of Buchner funnel set up

The next job is to remove any remaining water from your solid. Carefully scrape your solid into a small beaker using a spatula. Measure about 10cm3 of propanone in a measuring cylinder. Take great care not to spill propanone on your skin or get it in yours eyes. Donít sniff it, either. Pour the propanone into the beaker and stir the mixture with a stirring rod. Put a new piece of filter paper in the Buchner funnel. Filter the mixture as you did before.

Finally, you are ready to make the dried solid into an artistsí paint. Transfer the solid to a mortar. Grind it carefully with a pestle, and transfer it to a yogurt pot. Add just enough linseed oil to make a thick paint. Donít add to much at once! If the paint gets too runny youíve had it! When you use your paints, remember to wear gloves, and to seal your picture inside plastic when it is finished (it will take about 2 days to dry).

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Teacher notes

It is difficult finding safe chemicals from which to make paints. Red and yellow are especially tricky. For red, we have investigated using red lead, iron oxide or copper(I) oxide from the reaction between glucose and Fehlingís reagent. The first two are unsatisfactory because little chemistry is involved (just mixing and grinding), and it is difficult to achieve a significant quantity of red solid in the last one. For yellow, various chromates give good colours, but it can be unsafe to isolate the solids. As a result, we have settled on Prussian blue, a lead white (lead chloride) and a lead yellow (lead iodide). These still need to be treated with respect and, as with all our activities, the students wear eye protection, overalls and gloves. An additional precaution is to seal the final pictures in plastic.

The only major problem comes from students who use too much linseed oil. This makes a sloppy mess and is not suitable for painting. We have found that the students get better results when they paint onto rectangles of white hardboard (easily available from hardware stores) rather than onto paper.

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Technician notes

For 5 groups of students (making colours):

5 x 10cm3 measuring cylinders
5 x test tube racks
25 x boiling tubes
5 x wash bottles with distilled water
10 x plastic dropping pipettes

For 5 groups of students (making paints):

5 x 10cm3 measuring cylinders
5 x 100cm3 beakers
5 x glass rods
5 x spatulas
5 x pestles with mortars
5 x Buchner funnels
5 x Buchner flasks
5 x water pumps
filter paper to fit Buchner funnels
yoghurt pots

In the lab:

digital balances
marker pens
paintbrushes
pieces of hardboard

In the lab under teacher control:

iron(II) sulphate with spatula
potassium hexacyanoferrate(II) with spatula
lead nitrate with spatula
potassium iodide with spatula
sodium chloride with spatula

propanone labelled "Propanone - flammable"
linseed oil
white spirit

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