April 24, 2013
This report expresses five different pigments that were formed during chemical reactions. 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. 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.
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...