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newSchoolWorks.com › VoTechWorks › Agriculture, Environment & Public Service › Crime Scene / Forensic Technician › Bloodstain & Trace Evidence Basics › Lesson 10
AGR-CSI53-05 · Lesson 10 · 10.5 clock hours · practice

Soil and Paint Transfer Evidence

Objective. Students will collect soil and paint transfer samples in a manner that preserves their forensic value for class comparison and submit them with correctly completed documentation

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Why Soil and Paint Evidence Matter

Soil and paint are two of the most common types of trace evidence recovered at crime scenes. Both can place a suspect at a location, link a vehicle to a collision, or connect a tool to a forced entry. Because they are easily disturbed, contaminated, or lost, the way you collect, package, and document them determines whether they ever reach a courtroom.

Soil as Evidence

Soil is not simply "dirt." It is a mixture of minerals, organic matter, moisture, seeds, pollen, insects, and microscopic organisms that varies from one location to another — sometimes within a few feet. A forensic scientist can compare the color, texture, mineral composition, and biological content of a questioned soil sample against a known sample to assess whether they share a common source.

Collecting Soil Samples

Always collect a known sample from the specific location you believe transfer occurred (the source area) and a questioned sample from the object that may have picked up that soil (such as a shoe sole, tire tread, or shovel blade). Collect them separately and package them separately.

Use a clean wooden depressor or similar uncontaminated tool. Never use the same tool for two samples without cleaning it first — cross-contamination destroys evidential value. The paper druggist fold (also called a pharmaceutical fold) is the standard packaging method for soil: it allows moisture to escape, preventing mold growth that would alter the biological content. Never use plastic bags for soil — trapped moisture degrades the sample. Place the paper fold inside a labeled paper envelope.

For each sample, record:

Collect approximately one tablespoon of soil — enough for multiple analyses — but take only what the scene allows without unnecessary disturbance.

Paint as Evidence

Paint evidence is especially common in hit-and-run investigations, burglaries involving painted surfaces, and vandalism cases. When two painted surfaces contact each other, paint may transfer in one or both directions. The layer sequence of a vehicle's paint — primer, base coats, and topcoat — is distinctive and can be compared against manufacturer databases and known samples.

Photographing Paint Transfers

Before touching anything, photograph the transfer in context, then take close-up photographs with a scale reference. Document the location of the transfer on the object (e.g., "left rear quarter panel, 18 inches above the rocker panel").

Collecting Paint Chips

Use a clean scalpel or single-edged razor blade with forceps to carefully lift paint chips. The single most important rule is to preserve the layer sequence: collect chips intact rather than scraping them into powder. Place chips directly into a paper druggist fold, then into a rigid container such as a pillbox or small vial. Rigidity prevents the chips from being crushed and the layers mixed or broken. Do not use cotton swabs or soft packaging that can abrade the sample.

For each transfer site, collect separately. Label the container with the location, case number, collector name, date, and time. Complete an evidence submission form before the item leaves your hands.

Describing Evidence Without Drawing Conclusions

On a laboratory submission form, your job is to describe what you observed, not to interpret it. Write physical descriptions: color using a recognized reference (such as a Munsell soil color chart or an automotive paint color standard), texture (coarse, fine, sandy, clayey), approximate quantity, and the location and nature of the substrate. Do not write "this soil matches the suspect's yard" — that is a conclusion for the laboratory examiner. Write instead: "Brown-gray, fine-grained soil, approximately 5 mL, collected from left heel area of right shoe."

The Munsell Color System provides standardized hue, value, and chroma designations for soil color (for example, 10YR 4/3). Using a standardized reference makes your description reproducible and objective.

Safety

Chain of Custody

Every sample must be sealed and signed before it leaves the scene. Any gap in the chain of custody — an unsealed package, a missing entry on the submission form — can make the evidence inadmissible. Complete your forms in ink, never pencil.

Key terms8

Known sampleA sample collected from a source location whose identity is established, used as a reference for comparison against a questioned sample.
Questioned sampleA sample recovered from a person, vehicle, or object whose origin is unknown and must be determined through comparison.
Paper druggist foldA folding technique that securely contains small amounts of trace evidence in paper, allowing moisture to escape while preventing loss of the sample.
Layer sequenceThe ordered arrangement of paint coats — typically primer, base coats, and topcoat — whose specific pattern can identify a vehicle's make, model, or repair history.
Munsell Color SystemA standardized color notation system that describes soil color using three scales — hue, value, and chroma — allowing objective, reproducible color descriptions.
Trace evidenceSmall or microscopic materials transferred between a person, object, or environment during contact, including soil, paint, fibers, and glass fragments.
Chain of custodyThe documented, unbroken record of every person who collected, handled, transferred, or examined a piece of evidence from scene to court.
Cross-contaminationThe unintentional transfer of material from one sample to another, which can destroy the evidential value of both samples.
In class: Soil collection: students collect known soil samples from a designated outdoor area using a clean wooden depressor and paper fold method, then collect a questioned sample from a mock shoe sole; they label, package, and document the collection location with GPS coordinates and a sketch, and note environmental conditions · Paint transfer collection: using a pre-prepared mock vehicle panel with a smear of contrasting paint, students photograph the transfer, use a clean scalpel to collect paint chips in layers (preserving the layer sequence), package in a paper druggist fold inside a rigid container, and complete a submission form · Comparison exercise: students examine photographs of soil color charts (Munsell or equivalent) and paint chip color standard references and practice writing a physical description of their collected samples suitable for a laboratory request form
Materials: Wooden depressors, paper druggist fold sheets, glassine envelopes, rigid vials, clean scalpels, forceps, GPS device or phone with GPS, Munsell soil color chart or color reference, mock vehicle panel with paint transfer, camera, evidence submission forms
Check: Instructor reviews collected samples and submission forms: soil sample must be in paper (not plastic) and GPS coordinates must be recorded; paint chips must be packaged to prevent layer mixing; submission forms must describe the evidence using physical observation terms only (not conclusions); all three items must meet standard to pass

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Crime Scene Processing and Evidence Collection
1. A student collects a soil sample from a suspect's boot sole and places it in a sealed plastic zipper bag. What is the primary problem with this packaging choice?
Trace Evidence Recognition and Collection
2. When collecting paint chips from a vehicle involved in a hit-and-run, why is it critical to keep the layer sequence intact?
Evidence Documentation and Report Writing
3. A technician's soil collection notes read: 'This soil definitely came from the suspect's backyard.' Which statement best describes this notation?
Crime Scene Processing and Evidence Collection
4. Which packaging combination correctly follows standard protocol for a soil sample collected at a crime scene?
Trace Evidence Recognition and Collection
5. A student uses the Munsell Color System and records a soil color notation of 10YR 4/3. What does this notation communicate?
Health and Safety in the Field
6. When using a scalpel to collect paint chips in the field, which safety practice is most important?
Crime Scene Processing and Evidence Collection
7. A technician collects a questioned soil sample from a suspect's shoe sole and a known sample from the scene, but uses the same wooden depressor for both without cleaning it in between. What is the consequence?
Evidence Documentation and Chain of Custody
8. An evidence submission form is returned to a technician because the chain of custody is considered incomplete. Which situation most likely caused this rejection?
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