Paint Chips

By: Ameera Fatima and Jessica Hogle

Physical Properties

Basics:

-paint chips have various colors based on the amount of pigments

-paint can be very smooth and glossy or it can be more rough and matte.

-paint does not have a very good taste. most paints are non toxic if swallowed but it is not recommended that one taste paint

Film thickness:

  • thick films of densely packed pigment, the color will appear more saturated and deeper

  • film becomes thinner, the undertone becomes more pronounced and the overall color can appear more transparent

  • effects are ultimately caused by having an increased amount of light reflected from both the pigments and the underlying substrate

Pigment load:

  • altering the pigment load or density in a paint film can markedly change the perception of a color

  • densely packed translucent pigments, much of the transmittance of light can be lost through subsequent and repeated absorption and one primarily sees just the reflected light coming from the surface

  • pigment load is decreased, and light begins to penetrate through the film, the interplay of scattering and absorption has a larger impact on the overall color

Sheen and surface

  • surface is glossy or matte, smooth or textured

  • Surface impact a color’s expression

  • Glossier the paint= less scattering of light at the surface and more penetration and absorption of the light

  • darker color to typically appear deeper and more saturated when they have a gloss sheen, and conversely, appear to lighten if matte

Chemical Properties

Paint consists of 3 parts:

-pigments: a polyester film former play a large role in determining the color and appearance of paint. Pigments are a powder. In paint that exhibit a white hue, titanium dioxide is the main ingredient. In paints the express other colors, the pigments are selected to absorb only certain kinds of light, thus yielding a given color. Organic pigments yield the brightest colors, while inorganic pigments yield less bright but more durable colors

-binder: responsible for providing adhesion, binding the pigment, and also gives the paint resistance properties which make the final coating tough and durable. The binder itself is clear and glossy, but the presence of pigment interferes with this quality. Depending on the ratio of pigment to binder, or the PVC (pigment volume concentration) the paint can assume varying levels of glossy finish

solvent: liquid component of a paint is simply responsible for transporting the binder and pigment to the substrate surface. They tend to be either oil-based (high VOC (volatile organic compound) content) or water-based (low or no VOC content). Latex paint, which has lower VOC levels and is generally more environmentally friendly than oil-based paints. Oil-based solvents include white spirit, formaldehyde and toluene, along with a variety of other alcohols, ketones, acetates and aromatic compounds.








How do Forensic Scientist analyze Paint?

First, the scientists look at the appearance of the sample -- its color, thickness and texture. They examine the sample under a polarized light microscope to view its different layers. Then they can use one of several tests to analyze the sample:

  • Fourier transform infrared (FTIR) spectrometry determines the type of paint (chemicals, pigments, etc.) by analyzing the way in which its various components absorb infrared light.

  • Solvent tests expose the paint sample to various chemicals to look for reactions such as swelling, softening, curling and color changes.

  • Pyrolysis gas chromatography/mass spectrometry helps distinguish paints that have the same color, but a different chemical composition. The paint sample is heated until it breaks into fragments, and then is separated into its various components.

Case Study

Arsonists destroyed the library and partially damaged the sanctuary at the B’ Nai Synagogue in Sacramento, California on June 18, 1999. Many evidences were captured by the police such as 1- gallon Mobil oil jugs, torn fabric, wooden crates and many more things. The oil jugs had plenty of trace evidence on it. The paint chips that were found had a light blue top coat over a red layer. A month later, a couple was murdered on their bed while they were asleep. Another medical clinic which performed abortions near Sacramento was burned down. Many events like these were going on and the trace evidence was barely a help to link it back to a suspect. The break in the case came when the credit cards of the murdered victims was used to order ammunition from Arizona. The police located the delivery location and found Matthew Williams and James Williams picking up the ammunition. Their home and car was searched constantly and the police eventually recovered a weapon that murdered the couple. It was a black pry bar. The pry bar had shreds of glass and green paint. The synagogue did not have any green paint however, the medical clinic had a windows which had a green trim. A prior search at the brothers’ parents’ residence involved the collection of the same mobile oil jugs that were found at the synagogue fires. Therefore, the Williams brothers’ were found guilty in the case.


A City Unites After Synagogue Arsons