Materials Included In Kit

Additional Materials Required

Safety Precautions

Although casein and FD&C food dyes are considered nonhazardous, they may be irritating to body tissues and eyes. Do not ingest or get into the eyes. The dyes will stain clothing, skin and other materials. Sodium borate is slightly toxic by inhalation and ingestion. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding.FD&C food dyes may be stored for future use. Casein paint may be disposed of according to Flinn Scientific Disposal Method #26b. Sodium borate may be disposed of according to Flinn Scientific Disposal Method #26a.

Lab Hints

• Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students. All parts of this laboratory activity can reasonably be completed in two 50-minute class periods.
• The paint made in this lab may be used along with Styrofoam^® balls and toothpicks to make molecular models.

Teacher Tips

• The Glue-Making Kit (Flinn Catalog No. FB1578) is an excellent example of an alternative experiment using casein.
• Some surfaces students may paint on are paper, paper plates and blocks of wood.
• The paints can be covered with paraffin wax and saved.

Answers to Questions

1. Describe the appearance of the casein mixture as a finished product.

   The casein mixture has more fluidity when combined with borax. The material is more fully dissolved. An odor is not detected in the finished product. It does not contain the strong odors that are present in spray paints or latex paints.

2. Research other substances that contain casein. Give at least two examples.

   Casein is found in various types of cheese, yogurt, butter, etc.

3. Compare the casein paint to that of water color or oil paint you have used before. Does it cover the surface as well? How does the dried color/surface compare?

   The paint is smooth and glides over the surface. The dried color is glossy.

4. Give an example of a harmful chemical found in commercial paints.

   Spray paints contain hydrofluorocarbons. Acrylic paints contain formaldehyde.

   {12500_Answers_Figure_2}

References

The City of Tuscon Health and Safety in the Arts. Painting and Drawing techniques. http://www.tucsonaz.gov/arthazards/paint3.html (accessed January 2012).

The Old Fashioned Milk Paint Co., Inc. A Brief History of Milk Paint. http://www.milkpaint.com/about_history.html (accessed September 2011).

Wailes, Raymond B. How's It Made? Popular Science, March 1940, p 209.

Introduction

Milk is not only good for your bones, but it can also be used to make an environmentally safe paint! Create your own paint using casein, a protein found in milk.

Concepts

• Proteins
• Amino acids
• Green chemistry

Background

Proteins are fundamental biological compounds made up of linked molecules called amino acids. Amino acids differ slightly in molecular structure and therefore may exhibit unique chemical properties. The general structure amino acid (see Figure 1).

consists of an alpha carbon, an amino terminus, a carboxyl terminus and a side chain that is specific to each of the amino acids (R). Considered to be the building blocks of proteins, the carboxyl terminus (COOH) reacts with the amino terminus (NH₂) of amino acids and a peptide bond forms (see Figure 2). The nature of the peptide bond allows for many amino acids to be joined together to create the primary structure of a protein. Fascinatingly, proteins also form secondary, tertiary, and quaternary structures via other chemical bonding means.

The protein casein contains a primary structure made up of many charged, basic amino acids—histidine, arginine and lysine. In addition to its nutritional value, casein has been utilized as an adhesive and an effective, environmentally friendly paint. In fact, the ancient Egyptians used casein in glue and tempera. Casein acts as a water-soluble binding agent to hold the pigments and other ingredients together in the fast drying tempera paint.

Traditionally milk paint was made by isolating the casein protein from milk using acid. Casein exists in a salt form with calcium ions in milk. Upon addition of hydrochloric acid, the protein precipitates from milk and can be isolated. Casein contains negatively charged areas, hydrogen ions from the acid attach to these negative charges and casein becomes insoluble. The casein may be filtered from the liquid.

Milk paint is environmentally friendly because it is nontoxic. The materials in milk paint are made from the following organic raw materials: pigment, pure casein powder (or milk as starting material), and lime or borax. Many commercial paints are considered toxic because they can contain latex, formaldehyde and volatile organic solvents. Explore this environmentally friendly activity and create beautiful works of art with various color milk paints!

Experiment Overview

In this activity pure casein protein and pigments will be used to prepare an environmentally friendly paint.

Materials

Safety Precautions

Sodium borate is slightly toxic by inhalation and ingestion. Casein and the FD&C dyes are considered nonhazardous, but FD&C dyes will stain skin and clothing. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Part A.

1. Mix 15 g casein in 50-mL DI water in a 250-mL beaker. Cover with plastic wrap or Parafilm^® M and set aside for 20 minutes.

Part B.

2. Heat 50 mL of DI water in a 100-mL beaker, but do not bring to a boil.
3. Measure 6 g of sodium borate and dissolve in the warm (not boiling) water.
4. Add the sodium borate solution to the casein solution. Mix well with spatula.
5. Allow the mixture to sit for about one hour until all the casein has dissolved. The solution should have a translucent yellow appearance.

Part C.

6. Prepare a hot water bath using the 500-mL beaker.
7. Heat the casein mixture to approximately 60 °C using the hot water bath. The solution should have a consistency similar to syrup.
8. Remove the solution from the heat, place on a heat-resistant surface, and cool to room temperature.
9. Obtain a small beaker (25 mL) and add one small scoop of dye (about the size of a grain of rice) to the beaker.
10. Using a pipet, add 1 mL of DI water to the beaker and swirl to dissolve the dye.
11. Using a 25-mL graduated cylinder, add 15 mL of casein solution to the dye in the beaker. Stir with a rod to mix. (If necessary add more FD&C dye to achieve desired color.)
12. Repeat steps 9–11 to make four additional colors of milk paint.
13. Use your paint to create a work of chemistry art!
14. Consult your instructor for appropriate disposal procedures.

Student Worksheet PDF

12500_Student1.pdf