Preparation of Paints from Pigments and Binders
Now come the moment of truth! Will the pigments and binders you prepared in the laboratory combine? Good paints are uniform throughout or homogeneous mixtures called colloids. Colloids contain particles that are evenly distributed through a dispersing medium, and remain distributed overtime rather than settling out. The major difference between a colloid and a solution is the size of the solute particles. Colloid particles are generally clumps that are ten to 1000 times larger than typical ions or molecules dissolved in solutions.
In paint the dispersing medium is the binder. If the pigments remain suspended in the binders, there is a good chance that a usable paint will be made meaning that the when the mixture is applied to a surface it will cover the surface uniformly. If the pigment particles separate from the binder and settle out of the mixture an unstable system called a suspension was produced. . Suspension particles are generally 1000 times larger than the solute particles of a colloid. If such a mixture is applied to a surface, the paint will not uniformly cover the surface.
In this activity you will prepare paints form the pigments and binders you previously prepared as well as from commercially available artist’s quality pigments and determine which combinations of pigments and binders make the best paints.
Procedure:
1. The pigments you will work with are already proportioned in small plastic cups. Obtain three samples of each of the pigments you have been assigned.
2. Using a plastic pipette, add gum Arabic binder drop by drop to one of the pigment samples. With continuous stirring, continue to add the binder, to the pigment until a consistency is obtained that you believe will make a good paint.
3. Repeat Step 2 for the commericial and glue binders.
4. Repeat Steps 2 and 3 for your second set of pigments.
5. Paint a small sample of each of the prepared paints on the prepared data table. You will have to obtain paint samples from the other groups that were assigned the other pigments.
6. When all groups have their data table, cover each paint sample tightly and place them in your shoebox.
Conclusion Questions:
1. Of the paints you prepared, which combination(s) of pigment and binder mixed the easiest and gave the most homogeneous paint?
2. Does the choice of binder affect the color of the pigment? How?
3. Using your table, determine the combination of pigment and binder that makes the best paint. Explain your choice.
4. Using your table, determine the combination of pigment and binder that makes the worst paint. Explain your choice.
5. Which paint(s) produced an obvious film when dry?
6. Which paint(s) tended to “chalk”, that is did the pigment particles rub off easily?
7. Which paints seemed to dry the fastest? Which dried the slowest?
8. What properties should the pigments and binders have in order to be useful?
9. Do your paints appear to be solutions, suspensions or colloids? Decide for each paint and explain your decision.
10. If you were to create a paint for your personal use, what qualities would you want it to have? What would you use the paint for, and how would each quality enhance that use?
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Binders |
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Pigments |
Gum Arabic |
Commercial |
Glue |
Carbon Black |
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Fe2O3 |
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CaCO3 |
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TiO2 |
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Ultramarine Blue |
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Prussian Blue |
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CuCO3 |
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Chalk |
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