Paint Pigment

The History of Paint Pigments Chem 111-404 April 24, 2013 Introduction: This report expresses five different pigments that were formed during chemical reactions - Paint Pigment introduction. Three out of the total five reactions went through a metathesis, or double-replacment reaction. A metathesis reaction can be defined as “a chemical reaction in which an element or radical in one compound exchanges places with another element or radical in another compound. ” (Webster). The other two pigments underwent a neutralization reaction, which is “A reaction between an acid and a base that yields a salt and water. ” (Webster).

In both types of reaction two substances are being combined to form a new solution. The metathesis reaction produces a solution and a precipitate, while the neutralization reactions produces a water, a salt, and even carbon dioxide. What precipitates during these reactions are deemed our pigments. When these pigments are added to a paint binding agent they form paint. Pigment paints have been known to date back to the cave drawings as a way of keeping track of history. Their pre-modern paint binders usually comprised of watercolors, which was the mixing of water with the pigments, and even fat from animals.

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Most modern water paintings fade while the old cave paintings have kept their coloring. As time passed, these paint binders changed with the growing demand for paintings. Some binders developed to make lasting watercolors are gum arabic and even honey. These binders assist with the color uniformity and thickness of the watercolors. As time went on a new paint, casein, was discovered. This paint is primarily identified in the Egyptian paintings. Casein is “a protein found in milk”(DBClemons) that is good for painting surfaces such as canvases and walls.

In Colonial America “it was used to paint sets for theatre and opera productions. It’s dull sheen surface makes it ideal for use under bright light”(DBClemons). The third type of paint is acrylic. This paint is composed of the precipitate, water and an acrylic polymer to bind it all together. Acrylic paint is “desired by many people for their positive qualities, such as their ability to resist water after drying” (Upson) Acrylics also create a glossy and even shiny result relative to other paints While the three paints noted before are well known, egg tempura paint is not as recognized.

This type of paint was “replaced by oils during the renaissance in the mid-fifteenth and sixteenth century” (Douma). This paint is formed by mixing the yolk of an egg, some water, and pigment from the reactions. The viscosity of egg tempura generates an effect comparable to three dimensional impressions. Many of the old-fashioned paintings have a “highly finished appearance” (Douma). In this experiment, watercolor is the paint being used. A hypothesis for this lab was assumed: if the watercolor binder is mixed with the precipitates from the reactions, then the mixture will be a thinner, lighter paint.

Methodology: In this experiment, steps were taken to make the 5 different pigments. First, was the Chrome Yellow pigment. The pH was then measured. One milliliter of 0. 5M sodium chromate was mixed with one milliliter of 0. 5 M zinc sulfate. Next no more than 5 drops of 6 M sodium hydroxide was added to the solution. The liquid was then separated by filtering the solution. The precipitate was set aside ready for the completion of the experiment. Secondly, the Barium White pigment. One milliliter of sodium sulfate was added to a test tube and the color recorded.

Next one milliliter of barium chloride was added to the test tube. The solution was then placed in the centrifuge to separate the liquid from the precipitate. Finally, the clear liquid was decanted off the top and the precipitate placed onto filter paper. The precipitate was then stored for the completion of the experiment. Synthetic Malachite involved the third and fourth pigment. 5 milliliters of 0. 5M solution of copper sulfate was measured into a beaker. It was then combined with three grams of sodium bicarbonate. Once the reaction stopped, the solution was split in two equal parts.

The first half was filtered and stored for the completion of the experiment, while the other half was stored for a week, unfiltered. The next week the unfiltered solution in beaker was filtered and set aside for another week. The fifth, and final pigment, was Prussian blue. One milliliter of 0. 5 M iron (III) chloride was measured into a test tube. Then, 0. 25 M solution of potassium ferrocyanide was mixed in. They were then filtered, and left to dry. The next week there were four paint binding options: egg tempura, casein, acrylic, and water color or gum arabic.

This experiment used watercolor. The first step was to grind the pigment with water to make a stiff paste. Then, gum Arabic was added in a 1:1 ratio. Results: The data produced from the experiment demonstrates that when two solutions are mixed, they undergo a reaction that produces a pigmented or colored precipitate and also a liquid. The precipitate produced then can be fashioned into paint. In the first pigment, chrome yellow was produced. The yellow sodium chromate combined with the clear zinc sulfate created an orange liquid and a yellow precipitate.

This is a metathesis reaction that causes the solution to be neutralized. The addition of sodium hydroxide causes the solution to become more basic. After the solution was filtered it created a yellow solid, and when the precipitate was crushed up and gum Arabic was it created a yellow paint. The second pigment, barium white, started with the clear colored sodium sulfate. After adding the milliliter of barium chloride, the solution begins to bubble and fizz and form a white precipitate. After the solution is centrifuged, the precipitate at the bottom was a thick white paste.

Once it dried it became a white solid. When the gum Arabic, water, and the pigment were mized together it formed a white paint Thirdly, the synthetic malachite was made. When adding sodium bicarbonate to the copper sulfate, the chemical reaction produces cloudy blue mixture. Carbon dioxide is being produced which displays that this is a neutralization reaction. The solution was then split into two equal parts. The first part was filtered and set aside. After two weeks, the solid precipitate was added to the water and gum Arabic and created a watercolor paint.

The second half of the solution remained in a beaker. When dried, the precipitate was added to the water and gum arabic and formed a light blue watercolor pigment. The final pigment was the prussian blue. This pigment was formed by the combination of iron (III) chloride and potassium ferrocyanide. This caused a chemical reaction producing a blue solution and a dark colored precipitate. The solution was filtered leaving the precipitate to dry for the completion of the experiment. Then after the two weeks, the precipitate was added to the gum Arabic solution creating an indigo colored paint.

The picture below shows the use of the watercolor paints created in the lab. The watercolor paint is easy to paint with but tends to run along the page. Discussion: As described, the chemical reactions reacted as scheduled. In the metathesis reactions, the positive and negative ions switch partners and formed various new mixtures. The pigments that went through the metathesis reaction were: 1. School bus yellow * Na2CrO4 + ZnSO4 ZnCrO4 + Na2SO4 2. Barium white * BaCl2 + Na2SO4 BaSO4 + 2NaCl 3. Prussian blue * 4FeCl3 + 3K4Fe(CN)6 + Fe4(Fe(CN)6)3 + 12KCl The two acid-base reactions or double replacement;

CuSO4 + 2BaHCO3 CuCo3 + Na2SO4 + H2O + CO2 Because the products consist of water, carbon dioxide, and a precipitate it proves that this is a neutralization reaction. When the precipitates were added to the water and gum Arabic, they became fluid like, as was expected. The paint was very smooth, and thin compared to other paints. Although, the water color may have been the primary way of communicating in ancient days it is not the most recognized in the modern world. As a whole, the expected results of the reactions, pigments, and gum Arabic occurred as expected. References:

Douma, M. , curator. (2008). Pigments through the Ages. Retrieved April 12 2013 , from http://www. webexhibits. org/pigments/intro “neutralization reaction. ” Merriam-Webster. com. Merriam-Webster, 2011. Web. 12 April 2013. Clemons, David. “D B Clemons – Casein History. ” D B Clemons – Casein History. DB Clemos, 5 July 2010. Web. 12 Apr. 2013. <http://www. dbclemons. com/casein1. htm>. Upson, Margo, and Bronwyn Harris. “What Is Acrylic Paint? ” WiseGeek. Conjecture, 20 Feb. 2013. Web. 12 Apr. 2013. <http://www. wisegeek. com/what-is-acrylic-paint. htm>.

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