ccjs 301: trace analysis paint, glass and soil slide narration · pdf filebecause of the iso...

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CCJS 301: Trace Analysis Paint, Glass and Soil

Slide Narration

Okay, Welcome to a discussion on more paint analysis. This slide show covers paint, glass and soil.

And we will first discuss paint analysis.

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Slide Narration

There are usually two main ways paint comes into the crime lab. The first is vehicle accidents. Usually you're trying to establish hit each other, or that a car hit a person. And if you are lucky, and you get layers of paint, you can probably get to make, model, color, and maybe even assembly plant of vehicles which might have been involved in a hit and run. The other main way that paint comes into the laboratory is usually burglaries or robberies-- paint used to break and enter a house, and it's usually either paint that went from the house on to the pry bar or crowbar or whatever was used to break in, or paint from the breaking in object that was left at the house.

Now, there are three components of most paints. All paints have to have binders and pigments. And the binder does exactly what it sounds like. It binds everything together. It keeps it all together so that the color stays together, stays even, stays on your walls. Very important. The pigment is that part which gives you the color. Now, some paints also have extenders added. Extenders can do a few things. Extenders are usually added to darker colors to make them cover better, to increase the solid content of the paint so they cover more evenly and better, and they hide flaws behind them. Extenders can also be used to make the paint-- to

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Slide Narration

make it so that you're able to work with the paint longer for faux finishes and things like that.

Now, discussing automotive paints, because automotive paints really are the majority of paints which come into the lab. All cars, when they come off the assembly line, have four layers of paint on them. The bottom is the primer-- the electrocoat primer-- which, the electrocoat primer is needed because that binds to the metal of the car. Then on top of that you have a primer surface that attaches the paint to the primer-- the electrocoat primer. Next comes the base coat. The base coat is where you get your color, and there are usually a few layers of base coat. It's usually not just one layer of base coat. Then you have the clear coat, and the clear coat is the protective surface that goes over the base coat that gives the paint that hardness to it. Now, of course, you might end up with extra base coats and clear coats if you decide to have your car painted a different color. And of course, the more the car is painted, the more individualized it becomes.

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Slide Narration

How do we actually go about looking at paints? You start with a microscopic evaluation, and under the microscope you're looking at the color, the texture, and the color layer sequence. And it is the layer sequence that is so important. And although a lot of people talk about primer as "primer grey". Not all primers in the automotive industry are grey, and the greys that are used can be different dependent upon the manufacturer, so that's why it's so important that not only do you have the color of the base coat, but you also have the color of the primers. Now sometimes you get really lucky and the actual chip that you have of paint, you can put right back in the car from where it chipped off. That is known as a fracture match, and a fracture match is individual evidence, because, let's face it. What are the odds that an accident will occur and paint will flake off in exactly that exact same shape and size? Pretty low, right? Fracture matches are few and far between they are the gold standard for individualized evidence for paint, but they don't happen that often. Usually you have to perform a chemical analysis.

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Slide Narration

So, when I say "chemical analysis" what do I mean? Well, these are a few ways that we do it. One of the best ways is through pyrolysis gas chromatography. You need a very small sample, 20 micrograms. That is less than a milligram for the sample, and they have libraries that distinguish colors from each other because-- and paint formulations, the binders, the pigments, all that kind of stuff. Because, just like in fibers, where there are multiple, multiple paint formulations, the same thing happens in cars. There are many ways to get to electric blue for a color, and the different manufacturers have different ways of getting there. Another way that you can do chemical analysis is through infrared spectrophotometry. IR is also used in drug anaylysis

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As in other trace evidence examinations, you really need examiners who are experts, and it takes about two years to become an expert in trace analysis. And in some labs, there are people who can only do paint analysis their entire career, and sometimes they have to do multiple trace analysis because of the size of the lab and the size of the jurisdiction. There are color charts and standards of the paint binders, primers, everything available from the manufacturer, and the Royal Canadian Mounted Police has put out a database called "PDQ", which stands for Paint Data Query, and based on the chemical analysis and the color layer sequence, PDQ can set you not only make-- can give not only make, model, and year, of manufacture, it can also get you to the assembly plant. Because every assembly plant, even for the same manufacturer has a slightly different formulation of paint.

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Slide Narration

Here is an example of a questioned layering and a known. And you can see there are a lot of similarities between them, and you would expect the question, as it has been damaged in the accident, to not look exactly like our known or our standard, which has not been damaged in an accident.

And here is an example of the layers that would show up in paint analysis. As you can see, you can get multiple and multiple layers.

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Slide Narration

Ok, we are done with paint, now we will move on to glass analysis.

So, glass, its really good evidence. Its very difficult to destroy. Glass is usually transparent or translucent. Transparent meaning you can see through it and translucent meaning light and come through it. Glass is made up with fused inorganic materials. Usually start with sand, and different items can be added to get the glass to where you want it and glass is many shapes, sizes, colors, types

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Slide Narration

There are a wide variety of compositions because you think about it, you think about a Pyrex, for instance. The reason Pyrex can be baked in and works very well in a kitchen is because it has a high boron content. Same thing with lab glassware versus windows, which is usually soda lime with high calcium and sodium contents. Now, in recent years, because of the ISO formulations, a lot of glass has become rather standard. For instance, residential window glass. There aren't that many variations between the residential window glasses that are out there. Same thing for commercial window glass because of the ISO standards, but there is a lot of different kinds of glassware out there, which is what makes it good evidence.

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Slide Narration

Another thing that makes glass good evidence is that it breaks very easily, hard to destroy totally, but breaks pretty easily and you end up with very small fragments that are difficult to see which you would know if you ever stepped on glass. And it gets mixed up in the clothing of the perpetrators clothing and they don't realize it. And its pretty easy to discriminate using microscope examination doesn't destroy the glass which makes it pretty good evidence as well.

This is just a representation of if you find glass what can you do with it. Glass off a shoe, you can look at it under the microscope, you can determine refractive index, thickness, and even under the-- some microscopes you can determine elemental composition of it. You can also destroy some of the glass to determine elemental composition. Using density tubes you can determine the density of the glass. There are a lot of different physical characteristics of glass where you can differentiate it from other glass. Now, glass is usually class evidence, and usually you use glass to eliminate people. Yes, we have this piece of glass, but it doesn't match the burglary thing that we thought it did.

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Slide Narration

Now, when a projectile hits a large piece of glass such as a window, you end up with cracks in that piece of glass. You have radial cracks that start from the center and go out, you have concentric cracks which make circles-- concentric circles-- around the impact point, and then you have conchodial lines. And these allow you, looking at them under the microscope, to determine in which way the glass was-- in outside or the inside.

And these show these conchordial lines or conchordial fractures showing the direction of impact

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Slide Narration

And here is a picture showing radial and concentric lines. And you can see the radial lines emanate from the point of impact going out, and the concentric lines form circles around that point of impact.

And here is a photograph of impact. showing once again, the radial coming from point of impact out and the center fractures.

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Slide Narration

Now, one of the only ways, just like paint, to individualize glass-- it's very difficult to individualize glass unless you get a fracture match, which this is what this is showing. Because once again, what are the-- you know, what's the possibility that glass is going to break in exactly this way again? Fracture matches are the only way to individualize glass. When you're talking about glass, because glass is pretty standard from house to house to house, or business to business to business, it's only when you spend hundreds of thousands of dollars on special glass that you might have physical and chemical properties that are different from any glass out there. That's very unusual, and sometimes you will end up with etching patterns or stained glass where it's a lot easier to individualize and figure out that, yes, these ones were the same even without that fracture match. But usually to individualize glass you need the fracture match.

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Slide Narration

And our last topic I will discuss is soil analysis

Soil usually contains minerals, animal leavings, vegetable leavings, either from deceased plants, Deceased trees, roots, things like that. And you have various levels of decay within there. Between the animal animal leavings, the plants plants leavings, and all the minerals that happen to be in soil. There are some good physical characteristics that soil can give you between pH, color and particle size, and then sometimes you end up with pollen content and pollen experts are soil part but sometimes you end up with pollen it only comes from certain areas where its not common where in an area the body is dumped, or where you find a suspect. And when you're

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looking for the minerals in soil, you are looking at color, shapes, optical properties. So once again, a lot of soil analysis is completed the same way glass and paint analysis is starting with a microscope and going on to some kind of chemical analysis.

And this is an example of different types of soils, and you can see at the top are the question soil, and the bottom are our known soils, and when you take soils, you need to take a variety of soils from a variety of different locations close to the area from where you think the soil came from. Because even in the space of a few feet, soil can vary depending upon the animal content and the plant content.

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Slide Narration

So we have briefly touched on plant paint analysis, glass analysis, and soil analysis. And I hope you understand now why they are mostly class characteristics, mostly characteristics which eliminate people as opposed to being inclusionary. Usually for individualized evidence, you need a fracture match or something so unique, nothing else can match it. And trace evidence is very important because of the properties. If you have ten suspects and two detectives, and through trace analysis, you could eliminate eight of those suspects, you now have two suspects and two detectives, which is a much easier situation to deal with. So just because trace is only usually a class characteristic evidence, that doesn't mean that it is unimportant or does not contribute to solving crimes. Thanks for listening.

ccjs 301: trace analysis paint, glass and soil slide narration · pdf filebecause of the iso...

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