Photography of Luminol and Bluestar Enhanced Bloodstains
Written by Mark Vecellio   

Investigators have used Luminol to detect latent bloodstains for more than three decades. Luminol is a chemical reagent that reacts to hemoglobin in blood, causing chemiluminescence resembling a blue or violet glow. Bluestar Forensic, a more recent variation, uses a similar chemical reaction to create chemiluminescence. Both have been widely tested and studied and are generally known as the preferred search reagents when the objective is to locate trace amounts of blood. Researchers and practitioners have illustrated the following benefits:

 

• Detecting bloodstains under several coats of paint;

• Detecting small quantities of diluted blood (the specific dilutions vary considerably from study to study);

• Detecting bloodstains on a variety of dark-colored surfaces that obscure the visibility of blood;

• Detecting bloodstains after exposure to fire;

• DNA testing can be successful after exposure to the reagents, even with diluted blood samples.


Image 1. This image depicts Luminol-enhanced bloodstains taken during a murder investigation. The scene is the suspect's bathroom, where he cleaned up after committing the murder. Luminol application allowed investigators to locate minute traces of the victim's blood in and around the suspect's sink and shower.

For the investigator, however, it is important to realize that Luminol and Bluestar are presumptive tests. Anytime suspected blood is detected with these reagents, forensic testing in a laboratory must follow to confirm the substance is blood. In fact, numerous studies and case reports have revealed a variety of substances that cause false positive reactions.

Once Luminol or Bluestar is applied and a potential bloodstain uncovered, the chemiluminescence should be photographed to help ensure admissibility of the evidence in court. This photographic process requires a bit of specialized knowledge of camera function. This article will focus on helping investigators understand specific and necessary photographic requirements for both Luminol and Bluestar.

There are several articles and a few textbooks that provide guidance, but many are outdated, either relying on film-photography methods or already-antiquated digital technology. Recent technological advances in digital single lens reflex (DSLR) cameras allow for adjustments to camera settings that can help maximize light and thus reduce exposure time. Reduction of exposure time, resulting in a reduced time of Luminol/Bluestar application, may be helpful. Though numerous studies have shown that DNA testing can be successfully completed after use of Luminol or Bluestar, application of the reagents will dilute the bloodstains. This dilution may be problematic on vertical surfaces or near drains, since the blood evidence may flow. By reducing the volume of Luminol or Bluestar, less dilution will occur and will therefore yield a better chance at recovering a higher quantity of DNA.

Investigators generally use Luminol and Bluestar in dark environments. The presence of ambient light, especially when Luminol is used, will overpower luminescence created by the chemical reaction involving the test reagent and blood. You may find, however, that Bluestar application, in some instances, may result in luminescence even in the presence of dim lighting. Even so, since variables-such as blood dilution, target surface, and volume of blood-are numerous and not easily controlled, I recommend applying the reagents in full darkness. This will create a higher likelihood that you will be able to detect faint luminescence.

Recommended photographic equipment includes a DSLR camera, tripod or quadpod, remote shutter release, scales, flashlight, and a camera flash. Unlike fluorescence photography with an alternate light source, camera filters are not required; the camera will have no trouble capturing the luminescence with standard lenses.

I recommend configuring your camera to store the images in both JPEG and RAW formats, if possible. The RAW format stores the precise light data collected by the camera sensor, and thus may be useful to confront any legal challenges. A RAW file will allow more latitude in post-production and provides better quality. However, JPEG technology allows for noise reduction caused by high ISOs and will generally provide suitable images. Additionally, JPEG images are easier to view using a variety of software applications and they use less memory. Saving the image as both types will allow you to seize the advantages of both; just make sure to use a memory card with plenty of storage. SD cards with 32 or 64 GB of space are relatively inexpensive and will provide ample storage.

The Process
The first step in the process will be mixing the reagent. Some reagents, such as Bluestar tablets, will require several minutes to dissolve. Prior to using the reagent, you should allow your eyes to adjust to darkness. This will allow you to better detect faint, low-intensity luminescence. I recommend allowing 15 minutes for your eyes to adjust to darkness. If, during this time, you move back and forth between dark and light areas, wear dark red goggles, which will prevent your eyes from losing adaptation to darkness.

Prior to applying Luminol or Bluestar, affix your camera to a tripod. If you are searching a small area, then you can position the tripod accordingly. Otherwise, have the tripod set to a proper height to photograph the general area you are searching. Once a reaction occurs and suspected blood is located, you can then rapidly position the tripod.

Pre-focusing the lens will be helpful if you are searching a small area and know the potential location of the bloodstain. If necessary, you can focus the lens once the luminescence is detected, but this may require momentarily adding light to the scene.

Configure your camera settings to ensure a proper exposure.

A combination of f-stop, shutter speed, and ISO settings will be used to collect sufficient light to capture the luminescence and, in many instances, the background. Because of several uncontrollable variables-such as blood dilution, whether the blood has been cleaned, quantity of blood, interfering chemicals, and so on-you will need to exercise flexibility when applying camera settings. The scene and evidence will dictate the need. If you practice with your camera, you will become sufficiently competent and should have little trouble adjusting the settings as necessary.

F-stop — Because of the lack of ambient light, one should use a fast lens and wide aperture whenever possible. This combination will maximize the ability of the camera to collect light. A generally effective f-stop would be f/5.6; this will result in a relatively wide aperture and maximize collection of light. Understand, however, that this use of a wide aperture does not come without sacrifice. In this instance, the sacrifice will be depth of field, which is defined as the range of your image that is in clear focus. A wide aperture will result in a narrow depth of field, but depending on your scene and evidence, this may not be problematic. For instance, if your evidence and scene is in a small area (as is often the case with minute bloodstains), then a narrow depth of field will not be much of a concern. However, if your scene covers a long distance or items at various distances, then you should consider a smaller aperture. In these cases, I recommend at least an f-stop of f/8, but you may choose f/11 or f/16 depending on your scene. You will need to compensate for the loss of light by adjusting your shutter speed and/or the ISO. Many published articles and guidance do not advocate these higher f-stop numbers, but I've achieved satisfactory results in both training settings and actual casework. (Image 2)


Image 2. This image was taken with only a 5 second shutter speed, using f-8 and ISO 1600. Notice that the image allows both the luminescence and background to be visualized. The key is the addition of just enough fill light to illuminate the background without overpowering the luminescence. The higher than normally recommended f-stop will produce a better depth of field.

ISO — DSLR ISO settings refer to the camera sensor's sensitivity to light. Lower ISO numbers generally result in a higher-quality image, but are less sensitive to light. Higher ISOs, conversely, are better suited for low-light photography, but some degree of quality may be compromised. The standard highest-recommended ISO was once 400-but thanks to recent advances in ISO technology spanning many types of DSLRs, you will find that higher ISOs are suitable. What this means is that you will be able to use a faster shutter speed, and potentially less reagent. This should be the goal, since less reagent will result in less blood dilution. Different cameras use different ISO technology, so you should experiment with your camera to determine an acceptable ISO limit. Some cameras may produce sufficient images with ISOs of 3200 or even higher, while others may have a limit of 800 or less. (Note: Images 2 - 10 in this article were taken with a Nikon D5200.)

Shutter Speed — The shutter speed will ultimately depend on the f-stop and ISO selections, as well as the size of the scene and method of fill light. Ultimately, your familiarity gained from experience and practice will allow you to select a proper shutter speed based on conditions. You can view a series of effective shutter speed, f-stop, and ISO combinations in Images 3 - 6. Again, use of a higher ISO will allow much faster shutter speeds than recommendations provided in much of the available literature.


Image 3. This image was taken with a 20-second shutter speed, f/5.6, and ISO 1600.


Image 4. This image was captured with a 10-second shutter speed, f/5.6, ISO 800.


Image 5. This image was captured with a 6-second shutter speed, f/5.6, ISO 800.


Image 6. This image was captured with a 5-second shutter speed, f/8, ISO 3200. The ISO of 3200 is well beyond most recommendations, but I suggest you practice with higher ISOs to determine the highest setting that meets your image-quality requirements. Recent improvements in ISO technology have dramatically increased the quality of high-ISO images.

White Balance — White balance is a camera setting that affects how the colors in the image appear. The goal should be for the colors to appear "normal," as you observed them. Some types of lighting will cause unnatural coloration of your image. Fortunately, DSLRs have Auto White Balance settings that are effective for Luminol and Bluestar photography. I recommend using the Auto White Balance setting and only changing it if you detect a problem.

Once camera settings are configured, use a fine-mist sprayer to apply the Luminol or Bluestar over the search area. Once luminescence (positive reaction) occurs, collect a sample. Collection of the blood should be the top priority. Remember that these chemical reagents are presumptive in nature.

Position the tripod accordingly and activate the shutter, preferably using a shutter-release cable or wireless shutter release. This will help prevent blur caused from camera shake, a common problem in long shutter duration photography.

For mid-range images, use a fill light to add light to the scene. The goal is to capture the luminescence and the surroundings. Since the application of the reagent will occur in darkness, the fill light is required to reveal the scene itself. Otherwise, the image will only reveal the luminescent reaction in darkness, with no visualization of where the blood was located. Close-up, examination-quality images of fingerprints and footwear prints do not require fill light since the goal is to capture the fine details of the evidence. More details concerning examination-quality images is presented in a subsequent portion of this article.

I have found the most useful techniques for adding fill light to be use of an LED flashlight. When using a flashlight, quickly turn the light on and off a few times while the shutter is open. Aim the light at the ceiling relatively near the evidence, thus allowing the light to diffuse and gently brighten the area proximate to the luminescence. You should practice this technique using the specific light you plan to use at the crime scene. Small rooms and reflective surfaces will require less fill light than larger rooms and absorbent surfaces. Determining the proper amount of fill light is an art form that requires practice due to the wide number of variables: the size and surface substrates at the scene, and intensity of the luminescence and the light. With repeated practice, you should find it relatively straightforward to gauge the proper amount of light to add. Do not aim the fill light directly at the evidence; this will often overpower the luminescent reaction.

When photographing luminescent reactions in large outdoor scenes, you will add light to the scene. Though a flashlight can be effective for smaller outdoor scenes, large scenes pose difficulty. It is difficult to evenly apply fill light over large areas using a flashlight. Instead, you can use a camera flash to add the fill light. You will essentially use painting with light techniques by activating your camera flash at different positions, fully illuminating your scene-while, at the same time, not overpowering the luminescence. You may find, depending on your scene, that a lower flash intensity is preferred. Another option of fill light is a spotlight. You can pan the scene with the spotlight, filling in areas of darkness. This option works quite well, but again, will require practice to master. These large outdoor scenes will often require a longer shutter duration; you will need that extra time to fill in the large dark areas with artificial light. (See Image 7)


Image 7. This is an outdoor image of luminescence. A camera flash was used as fill light. I recommend you practice with this technique in order to determine the best flash exposure. A 1/8 power flash was used in this image.

Examination-Quality Images
Bloodstain pattern evidence, such as footwear prints and fingerprints, may be used by forensic scientists for comparison. Images of such evidence are referred to as examination-quality images. Specific camera settings and photographic techniques are mandatory to ensure these images are free of distortion and suitable for comparison.

All examination-quality images should follow some basic rules: use low ISOs, such as ISO 100, to ensure high quality; position the camera lens at a 90° angle to the evidence; fill the viewfinder with the evidence; and use a close-up or macro lens.

For Luminol/Bluestar enhanced examination quality images, I recommend using an f-stop of f/8. This will allow sufficient depth of field (in instances where that is an issue), while maximizing light. This, of course, will necessitate a slow shutter speed, such as 30 seconds. The inherent problem with a slow shutter speed is potential dilution and flowing of the bloodstain, which will destroy the features of the evidence (Images 8 - 9). For this reason, I recommend using a reagent that is less prone to running. Bluestar Magnum is one such product. When applied with a fine-mist sprayer, such as the Bluestar Ecospray micro-sprayer, the reagent will allow a suitable examination quality image to be exposed (Image 10). Another option, as documented by author Edward Robinson in Crime Scene Photography, 3rd edition, is use of a blood stabilizer, such as sulfosalicylic acid. Robinson recommends a 3:1 Luminol-to-sulfosalicylic acid combination to both fix the blood and allow for luminescence.


Image 8. This image depicts a common problem associated with the use of Luminol and Bluestar: dilution and running of blood, especially on vertical surfaces.


Image 9. Bluestar was used in an attempt to capture this latent footwear print in blood. Unfortunately, the liquid mixture destroyed the pattern.


Image 10. This latent footwear print was enhanced with Bluestar Magnum and Ecospray micro-sprayer. This combination of reagent and fine-mist sprayer prevented destruction of the print and should be considered an alternative to regular Bluestar or Luminol when you believe pattern evidence may be present.

You should consider placing a scale along the print, as you would with any other examination quality image. Adding dim fill light with a flashlight will allow visualization of the scale without overpowering the luminescence.

Once you take your image, be sure to check it for both exposure and image sharpness. If necessary, adjust the camera settings and re-take the image. Remember that practice will reduce the number of re-takes.

Step by Step Summary
Remember to allow approximately 15 minutes for your eyes to adjust to darkness before beginning. This will result in an improved capability of detecting low intensity luminescence.

Step 1. Mix the reagent. Some reagents may require several minutes for tablets to fully dissolve.

Step 2. Affix your camera to a tripod. Have it prepared and ready to photograph. Pre-focus your lens if practical.

Step 3. Preset the camera to the preferred f-stop, ISO, and shutter speed, based on the requirements of your scene.

Step 4. Apply the reagent using a fine-mist sprayer. Once initial luminescence occurs, place the camera and tripod in position, enabling you to capture the luminescence as well as the surrounding area (for mid-range images). If you are taking an examination-quality close-up image, position the tripod in a manner that allows you to fill the camera viewfinder with the evidence. Make sure the camera lens is positioned at a 90° angle to the evidence to prevent distortion. Position a scale along the print.

I recommend, in most instances, collecting samples of the suspected blood prior to photography. An exception would be an examination-quality image, such as a footwear print. Collecting a sample from the print would obviously disrupt the footwear patterns. In such cases, collect the blood sample after the image is taken.

Step 5. Preferably using a remote shutter-release to prevent camera shake and subsequent blur, activate the shutter release to take the image.

Step 6. While the shutter is open, add fill light through use of a flashlight (indoor scene) or flash (large, outdoor scene). This will allow both the background and the luminescence to be captured. If you only wish to photograph the luminescence, then do not add fill light.

Step 7. Review your image and re-take if necessary. Remember that practice will allow you to hone this skill and reduce the necessity of re-takes.


About the Author
Mark Vecellio is an Assistant Professor of Applied Forensic Science at Methodist University in Fayetteville, North Carolina. He has 25 years of experience in the field of criminal investigations, crime scene investigations, and applied forensic science training. Vecellio retired from the U.S. Army's Criminal Investigation Division, where he served as a supervisory special agent and forensic science officer. He co-authored Pocket Guide to Crime Scene Photography, a text targeting novice crime scene photographers.

About the Photographers
Images 2 - 10 were taken by Sarah Morello, Kristee Emmons, and Lisa Kasamba, all Methodist University Applied Forensic Science students, engaged in various research projects involving Luminol and Bluestar.

 
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