This Halloween try out some forensic science experiments at home

Veronica McKinny is a PhD student at the Leverhulme Research Centre for Forensic Science and is using soft matter physics – the study of how soft, squishy things change over time – in forensic applications. She is looking at the behaviour of drying blood through this physics lens which will lead to new techniques to gain more information from crime scenes where blood is present.

Blood is not like water, it is a non-Newtonian fluid which means its viscosity changes depending on how much stress is placed on it. It was determined that this recipe (made from ingredients you can find at home) creates a blood substitute that behaves in similar ways to the real thing.

Creating realistic-fake blood alternatives is important for scientists to study blood and when forensic scientists are training. Be warned – this might get messy!

To make the realistic fake blood you will need

Materials

• Paper
• Kitchen roll
• Spoons
• Tap water
• Strawberry Angel Delight mix
• Chocolate Sauce
• Red food dye
• Optional: blue or black food dye for extra colour accuracy

Set-up

1. Creating your fake blood:
   1. Combine 90mL of water with 5g of strawberry Angel Delight mix.
   2. Add several drops of red food dye (roughly 2mL)
   3. Mix well. If the colour is not what you desire, you can continue to add red food dye 1-2 drops at a time, or you can add small amounts of blue or black food dye to try to get closer to the hue you’re looking for.
      1. Note: There may be small bits of stuff that are stuck at the top of the mix. If you have time to prepare the mix well in advance, these bits should be dissolved within 2-3 hours of being left to sit at room temperature.
2. Dying the water red:
   1. Fill a cup/mug/bowl with water.
   2. Add a few drops of red food dye. Optionally add blue or black food dye as well.
   3. Mix.
3. Set up some sort of inclined surface somewhere it’s easy to clean up a mess. i.e. prop a cutting board up on some tins/boxes.
4. Place containers of your fake blood, dyed water, and chocolate sauce next to your inclined surface.

The Experiment

1. Put one sheet of paper on your inclined surface and lay one sheet of paper flat on a surface nearby.
2. Use spoons to place one small droplet of each the fake blood, the dyed water, and the chocolate sauce at the top of the paper on the inclined surface, one at a time.
   1. Watch how the droplets of each of the substances move down the paper. How far does each go?
3. Use spoons to place one small droplet of each the fake blood, the dyed water, and the chocolate sauce on the flat piece of paper. Write down the time next to them.
4. Let the droplets dry. Every 30-60 minutes, come back and look at both sets of droplets. If you are interested, take pictures of the droplets each time you check, or lay down new droplets with their new time so you can compare different stages of the drying process. How are the droplets changing over time?

Questions to ask yourself

• Which of the three do you think is closest to real blood? Why?
• How do the different substances absorb into the paper differently? Why do you think that is?
• What patterns or colours differ between the three droplets as they dry?

If you have any questions please ask us on social media or email at LRCFSPublicEngagement@Dundee.ac.uk

Find out more about why Blood Pattern Analysis is important to forensic science and try a Blood Spatter experiment