Introduction: DIY Magnetic Applicator for Latent Fingerprint Development

About: I have too little time and too many hobbies.

Even though there are many forensic science shops in the States, it may be frustrating to find things in your country (like in my situation).

If you want to do your own forensic science experiments, the best way to start is latent fingerprints.

So first of all, what's a "latent fingerprint"?

According to Wikipedia; although the word latent means hidden or invisible, in modern usage for forensic science the term latent prints means any chance or accidental impression left by friction ridge skin on a surface, regardless of whether it is visible or invisible at the time of deposition.

There are tons of methods to develop latent fingerprints, such as dusting, fuming, ninhydrin or iodine treatments. All of these methods are used in different situations.

What we're going to make in this instructable is a "magnetic applicator" to use with a magnetic powder, to develop prints on porous surfaces, such as paper, cardboard, wood and even an orange.

Magnetic powder is way too heavy to apply with a fiber brush (the one you see on CSI) or a maribou feather duster. So it has its own applicator, which uses magnetism to form a ball of magnetic powder (which substantially looks like a brush).

In the next step, we'll talk about the few items we need to make one.

Step 1: Materials

This instructable is inspired by a disposable applicator called "The Tex Magnetic Wand System". (The 1st picture)


  • 1 Plastic Pipette (The one on the second picture)
  • 1 Neodymium Magnet - 6mm dia, 5mm thick (Smaller ones works too, but you'll need to use more than one)
  • A plastic or wooden dowel about the same diameter with the magnets (I'm going to use a paint brush handle)
  • Some tape (You can use any kind of tape)
  • Optional: Shrink tubing
  • Optional: X-acto knife or something similar to cut the dowel
  • Optional: Magnetic Powder (You can use neodymium powder or even printer toner)

That's it. Let's start!

Step 2: Make the Outer Shell

The outer shell is there to prevent the magnetic powder from sticking to your applicator. So, after using the powder, you can retract the handle back to let the powder drop back to the jar.

But there's a problem. When you retract the handle back, the magnetic powder tends to follow it. So, we'll need something to prevent this.

Start by cutting a few centimeters from the pointy side. Try to put your dowel into the opening to check if they fit. If it's too small, you can cut a few centimeters more. If the opening is too big, you can use some sticky tape to enlarge the diameter of the dowel you're using.

After that's done, we have to make the round tip of the pipette a little bit thicker to give the magnetic powder escape the magnetic field and fall back to the jar.

To do this, just use some sticky tape.

PS: Please excuse the mess on the cutting board, it's very old and has thousands of tiny paper bits engreaved to it :)

Step 3: Make the Magnetic Rod

As you see in the picture, my dowel was a little bit thin for the opening, so I widened it using some sticky tape. To make the rod, just glue your magnet to the top of the rod using super glue. I used some shrink tubing here, since I didn't have any super glue.

Step 4: Enjoy Your Magnetic Applicator!

Yup, that's it! Just put the dowel into the outer casing and you're good to go!

The first picture shows the original TEX Applicator and the second one shows the one we just made, pretty cool, isn't it?

And there's a video too to show you how to use it.

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