When blood is involved, fingerprint processing gets more complicated. Knowing how to process bloody surfaces without compromising ridge detail—or washing away the stain itself—is essential for preserving evidence. This guide walks you through best practices, chemical options, and documentation tips so you can handle bloody prints the right way.
If you’ve ever found yourself staring over a blood-stained surface, wondering how do I process a bloody surface without losing latent prints?—you’re in the right place! In this guide, we’re walking through a clear, actionable workflow so you can tackle even the messiest scenes with confidence.
Let’s dive in!
Step 1: Initial Assessment and Safety Precautions
Before you reach for your processing tools, step back and access the item with intention. Visual examination is your first—and most critical—move.
Key Actions:
- Observe before you act. Identify the location and condition of bloodstains—types of bloodstains present, wet vs. dry bloodstains, patent (visible) or latent (not visible) bloody prints.
- Suit up! Always wear PPE: gloves, gown, and mask.
- Plan your approach. Determine if the blood requires a presumptive test before moving forward. Decide if DNA collection should be prioritized before any processing begins or if the bloody prints take priority.
Presumptive Tests for Blood:
- Phenolphthalein (Kastle-Meyer)
- Tetramethylbenzidine (TMB)
- Leucomalachite Green
- Hemastix
These quick field tests can suggest the presence of blood, but they’re not always accurate. False positives can occur, so results should always be verified later at the lab with confirmatory testing and DNA analysis.
Step 2: Prioritize Photography First
In evidence processing, the “Golden Rule” is to work from least destructive to most destructive methods. When dealing with bloody prints, that means starting with thorough documentation before any enhancement or chemical processing begins.
Photography Tips:
- Start with natural light: Search the evidence without any enhancements.
- Use oblique lighting: Shine light from an angle to highlight faint ridge patterns.
- Use an Alternate Light Source (ALS): Infrared (IR) is especially useful for visualizing bloody prints on dark or patterned surfaces.
- Photograph any visible ridge detail: Capture 1:1 images in RAW format to preserve detail.
Don’t forget to include scales and identifying markers for every photo!
Step 3: Evaluate the Surface Type
Before selecting any enhancement method, identify what kind of surface you’re working with. Chemical choice depends heavily on surface type—using the wrong one could damage the evidence or yield poor results.
Surface Categories:
- Non-Porous: Glass, painted wood, plastic
- Porous: Paper, cardboard, unfinished wood
- Semi-Porous: Glossy magazine pages, coated paper, varnished wood
- Adhesive Surfaces: Tape, labels, sticky notes, stamps
Knowing the surface type will directly influence which blood enhancement chemicals you should choose.
Step 4: Choose the Appropriate Blood Enhancement Reagent
Not all bloodstains are created equal—and neither are the chemicals used to enhance them. Selecting the wrong reagent could turn a potential ridge detail into a ruined smear. To preserve and enhance blood evidence effectively, you’ll need to match the chemical to the surface, condition, and context of the stain.
Key Factors to Consider:
1. Substrate Type (Porous vs. Non-Porous):
Porous surfaces (like fabric or wood) absorb liquids, so choose a reagent that penetrates and develops detail. Non-porous surfaces (like tile or glass) require reagents that sit on the surface and provide contrast without smearing.
2. Contrast Needs:
Consider the background color and texture. Some reagents provide visible color stains (ideal for light backgrounds), while others fluoresce under alternate light sources (helpful on dark or complex backgrounds).
3. Work Environment:
Field applications often require fast, easy-to-use chemicals. In the lab, you have more control over variables, making reagents other reagents more practical.
4. Target Material:
Some reagents react with proteins in blood, while others target heme. Understanding what you’re enhancing helps narrow down the right chemical.
5. Stain Condition:
Wet, dry, faint, or degraded stains may respond differently. Dry, faint stains often need more sensitive reagents, fixatives, or less destructive documentation with an ALS.
Should You Use a Fixative?
A blood fixative is applied before the enhancement reagent to stabilize the stain and prevent distortion. This is especially important for fragile or faint bloodstains, or when using liquid-based chemicals that risk washing away detail. Whether or not to apply a fixative depends on:
- The chemical composition of the reagent (e.g., aqueous or alcohol-based).
- The target matrix (protein vs. heme).
- The substrate type (porous vs. non-porous).
- The condition of the bloodstain (wet, dry, faint, or compromised).
Popular Blood Enhancement Chemicals:
| Reagent | Best For | Reacts With / Stains | Color / ALS Wavelength |
| Acid Fuchsin (Hungarian Red) | Light-colored, non-porous surfaces | Stains proteins in blood | Red-pink color; fluorescence at 450–490 nm |
| Acid Yellow 7 | Dark-colored, non-porous or semi-porous surfaces | Dyes proteins in blood | Fluorescence at 450–490 nm |
| Amido Black | Light-colored, non-porous or semi-porous surfaces | Stains proteins in blood | Dark blue-black color |
| Coomassie Blue | Light-colored, non-porous surfaces | Stains proteins in blood | Deep blue-purple color |
| LCV (Leucocrystal Violet) | Non-porous and semi-porous surfaces | Reacts with the heme group in hemoglobin | Deep purple color |
| Merbromin | Non-porous and semi-porous surfaces | Dyes the heme group in hemoglobin | Fluorescence at 365-380 nm |
Pro Tip: Always test your reagent on a small, non-critical area if possible.
Step 5: Capture Post-Processing Images
As soon as your bloody prints have developed, it’s time for another round of photography.
Tips for Effective Photography:
- Use Multiple Light Sources: Capture in both natural and alternate light (ALS), if applicable.
- Include Scales & Labels: Always.
- Document Settings: Camera model, lighting, exposure—your future self (and your case file) will thank you.
Don’t Forget the Blood Reagent Expiration and Shelf Life!
When was the last time you checked your chemical cabinet? Old or improperly stored blood enhancement chemicals can ruin evidence. Use this table as a quick reference:
| Reagent | Shelf Life of Working Solution | Storage Conditions |
| Acid Fuchsin (Hungarian Red) | Use within 3 months | Store in an amber bottle in a cool or refrigerated location |
| Acid Yellow 7 | Use within 1-2 weeks | Store in an amber bottle in a cool or refrigerated location |
| Amido Black | Use within 3 months | Store in an amber bottle in a cool, dry and dark location |
| Coomassie Blue | Use within 3 months | Store in an amber bottle in a cool, dry and dark location |
| LCV (Leucocrystal Violet) | Use within 1 month | Store in an amber bottle in a cool or refrigerated location |
| Merbromin | Use within 6 months | Store in an amber bottle in a cool or refrigerated location |
Pro Tip: Always label reagents with mix date and expiration. Follow your lab’s SOPs for storage and disposal.
⚠️ Disclaimer: This information is intended as a general reference and does not replace manufacturer recommendations. Always refer to the manufacturer’s guidelines and the chemical’s Safety Data Sheet (SDS) for specific storage, handling, and shelf life information. We are not responsible for misuse or misapplication of chemical reagents.
Conclusion: Why Methodical Processing Matters
Processing bloody latent prints isn’t just about following steps—it’s about honoring the integrity of the evidence. Every action you take can either preserve the truth or bury it.
By approaching bloody surfaces methodically, choosing the right blood enhancement chemicals, and documenting thoroughly, you’re ensuring that the evidence has the best chance to tell its story.
Ready to take your latent print processing skills to the next level?
Level Up Your Bloody Print Processing!
Join us live on May 21 for our free webinar:
Enhancing Bloody Prints: A Blueprint for Chemical Selection and Documentation
Walk through real-world challenges of developing and documenting bloody prints with our expert instructors. Whether you’re just getting started or want to sharpen your skills, this live session will help you:
✅ Understand how blood composition affects enhancement
✅ Choose the right chemical based on surface, contrast, and safety
✅ Prepare evidence for clear documentation under visible and ALS lighting
Bonus: Get a sneak peek at our newest field-ready tools, including mini-courses and quick-reference guides for six major blood reagents.
Can’t make it live? No worries—you’ll get access to the replay, too.
Related Reading:
- Top Blood Enhancement Chemicals for Latent Prints
- Searching for Bloody Latent Prints: Tips for Vertical and Horizontal Surfaces
- Field vs Lab: Where Should You Use Which Blood Reagent?
- Do Your Blood Reagents Expire? Here’s How Long You Have
