Magnetic Slime: Creating a Responsive Non-Newtonian Fluid with Iron Filings
What Makes Slime Respond to a Magnet?
Magnetic slime is a polymer-based mixture that becomes responsive to magnetic fields when you suspend ferromagnetic particles, typically iron filings or iron oxide powder, throughout its structure. The slime base acts as a non-Newtonian fluid, meaning it behaves differently under stress (flowing when you pull it slowly but snapping when yanked quickly), while the embedded iron particles align themselves along magnetic field lines when you bring a strong magnet nearby. This combination creates a material that appears to "crawl" toward magnets, climb up their surfaces, and even engulf them entirely if given enough time.
The science here involves two separate phenomena working together. First, you're making a cross-linked polymer network, the slime itself, by triggering a chemical reaction between polyvinyl acetate (found in white glue) and a borate ion source (borax or liquid starch). This creates long, tangled chains that slide past each other under gentle force but resist sudden movement. Second, you're distributing tiny pieces of metallic iron throughout this network. When a magnetic field passes through the slime, those iron particles experience an attractive force and try to migrate toward the magnet, dragging the surrounding polymer matrix along with them.
The result is genuinely fascinating to watch, especially if you've never seen a fluid appear to have a "will of its own" before. Kids tend to describe it as "alive," which isn't far off as a metaphor, the slime moves, stretches, and responds to external stimuli in ways that seem almost purposeful.
Materials & Cost Breakdown
Here's what you'll need to create a functional batch of magnetic slime. Prices reflect typical retail costs as of early 2026, though you may find better deals buying in bulk or shopping sales.
| Material | Quantity Needed | Estimated Cost | Where to Find It |
|---|---|---|---|
| White School Glue (PVA) | 8 oz (1 bottle) | $2–4 | Grocery, craft store, online |
| Borax Powder | 1 tsp | $5–7 for 76 oz box | Laundry aisle |
| Warm Water | 1½ cups total | Free | Tap |
| Iron Filings | 2–3 tablespoons | $8–12 per container | Science supply, hardware store |
| Mixing Bowl (disposable or dedicated) | 1 medium | $1–3 | Kitchen supply |
| Wooden Stir Stick or Spoon | 1 | $1 or free | Kitchen, craft store |
| Nitrile or Latex Gloves | 1 pair per person | $0.50–1 | Pharmacy, hardware store |
| Neodymium Magnet (strong) | 1 or more | $5–15 | Hardware, online |
| Resealable Container | 1 | $2–4 | Kitchen supply |
Total estimated cost: $24–50 for your first batch, depending on whether you already have some items on hand. Subsequent batches drop to around $3–5 each since you'll have most materials left over.
Alternative Ingredient: Liquid Starch
If you prefer not to work with borax, you can substitute liquid starch (found in the laundry aisle) as your activator. Use roughly ⅛ cup of liquid starch per ¼ cup of glue. The texture will be slightly different, often a bit firmer, but the magnetic response remains identical. Iron oxide powder can replace iron filings for a smoother, darker slime that doesn't rust as quickly, though it typically costs more and may produce a weaker magnetic effect.
Step-by-Step Assembly Instructions
Phase 1: Prepare Your Borax Solution
Start by creating your activator solution. Measure 1 cup of warm water (not boiling, just comfortably hot from the tap) and pour it into a small bowl or measuring cup. Add 1 teaspoon of borax powder and stir thoroughly until the white crystals dissolve. This may take 30–60 seconds of continuous stirring. You'll know it's ready when the water looks clear with no visible particles settling on the bottom.
Set this solution aside, you won't add it immediately. The borax solution can be made ahead of time and stored in a labeled container for up to a week if you're planning multiple batches.
Phase 2: Mix Your Glue Base
Pour the entire 8-ounce bottle of white glue into your medium mixing bowl. Add ½ cup of warm water directly to the glue and stir until the mixture becomes smooth and uniform. The glue will thin out considerably, which is exactly what you want, this dilution makes the final slime easier to manipulate and ensures the iron filings distribute evenly rather than clumping.
Take your time with this step. Any unmixed globs will create weak spots in the final product.
Phase 3: Incorporate the Iron Filings
Measure 2–3 tablespoons of iron filings and pour them directly into your glue mixture. This is the messy part, so consider doing it over a tray or newspaper. Stir vigorously for at least 60 seconds, making sure the filings disperse throughout the white glue rather than sinking to the bottom. The mixture will turn a dark gray color and develop a slightly grainy texture.
Safety note: If you have sensitive skin or any cuts on your hands, this is the moment to put on your gloves. Iron filings can be irritating, and you're about to get hands-on with this mixture.
The filings will initially seem to resist mixing, clumping together in spots. Keep stirring. Use a folding motion, scraping the bottom and sides of the bowl, then turning the mixture over itself, to break up any clusters.
Phase 4: Activate the Polymer
Now comes the transformation. Slowly pour your borax solution into the glue-and-iron mixture while stirring continuously. You'll notice the texture change within seconds, the liquid suddenly becomes stringy, then cohesive, then almost solid. Keep stirring until the slime pulls away from the sides of the bowl and forms a single mass.
This reaction happens because the borate ions create cross-links between the long polymer chains in the glue, turning a liquid into a semi-solid network. The iron filings get trapped within this network, distributed throughout like raisins in bread dough.
Phase 5: Knead and Test
Pull the slime out of the bowl (it should come out as one piece) and knead it with your hands for 2–3 minutes. This accomplishes two things: it distributes any remaining borax solution evenly, and it works out excess moisture that might make the slime too sticky. If the slime feels wet or leaves residue on your fingers, keep kneading. If it feels too stiff or begins to crack, you can add a few drops of water and work it in.
Once the texture feels right, smooth, slightly stretchy, not sticky, test its magnetic properties. Hold a strong neodymium magnet near (but not touching) the slime surface. You should see the slime deform toward the magnet, creating a spike or tendril that reaches upward. Move the magnet slowly and the slime will follow. Place the magnet directly on top of the slime and watch as the material slowly engulfs it, appearing to "eat" the magnet over the course of several minutes.
If you're not seeing much movement, your magnet may not be strong enough. Standard refrigerator magnets won't work well for this experiment, you need the pulling power of a rare-earth magnet.
The Science Behind the Movement
Non-Newtonian Fluid Behavior
Your magnetic slime exhibits non-Newtonian characteristics, meaning its viscosity (resistance to flow) changes based on the force applied to it. Pull it slowly and it stretches like taffy. Yank it quickly and it snaps like a solid. This behavior comes from the polymer chains created during the borax-glue reaction. Under gentle stress, these chains have time to slide past each other. Under sudden stress, they can't rearrange fast enough and behave more like a solid.
This property makes the slime particularly interesting when combined with magnetic forces, which apply continuous, gentle pressure rather than sudden impacts. The slime responds by flowing slowly toward the magnet, but if you try to pull it away quickly, it resists.
Magnetism and Ferromagnetic Materials
Iron filings are ferromagnetic, meaning they can be magnetized by exposure to an external magnetic field. Each tiny particle contains magnetic domains, regions where the atomic magnetic moments are aligned in the same direction. Normally, these domains point in random directions and cancel each other out. But when you bring a magnet close, the domains within each iron particle align themselves with the external field, and the particle becomes temporarily magnetic itself.
This induced magnetism creates an attractive force between the iron particles and your magnet. Since the particles are embedded in slime rather than free-floating in water, they can't move independently, they have to drag the surrounding polymer network along with them. The cumulative effect of thousands of tiny particles all pulling in the same direction creates enough force to move the entire mass of slime.
The magnetic field also extends beyond the magnet's surface, forming invisible lines of force that curve through space. Iron particles throughout the slime align themselves along these field lines, which is why the slime often forms spikes or fingers pointing directly at the magnet rather than just moving as a formless blob.
Safety Protocols and Handling Guidelines
During Construction
Wear gloves throughout the mixing and kneading process, especially if you have any skin sensitivities. Iron filings can cause minor irritation, and some people react to prolonged borax exposure. Work in a well-ventilated area and keep the materials away from your face, you don't want iron dust near your eyes or mouth.
If you're working with children, supervision is recommended throughout. Kids ages 8 and up can typically handle the mixing process with guidance, but younger children should observe rather than participate in the iron-filing stage.
During Play
Once the slime is complete, it's fairly safe to handle with bare hands for short periods, though keeping gloves on remains the more cautious choice. The main risk comes from potential ingestion, this is not food, and the iron filings make it particularly dangerous if swallowed. Keep pets away from the work area and wash hands thoroughly after play.
The iron filings will begin to rust if exposed to moisture over time, which can discolor the slime and potentially cause irritation. Store your magnetic slime in an airtight container when not in use, and discard it if it develops orange spots or begins to smell metallic.
Magnet Handling
Neodymium magnets are powerful enough to pinch skin if two snap together unexpectedly. Keep them separated during storage, and never allow children to put them near their mouths or noses. These magnets can also erase credit cards and interfere with electronic devices, so maintain a safe distance from phones, computers, and wallets during your experiment.
Expected Results and Variations
A successful batch of magnetic slime should respond noticeably to a strong magnet held 1–2 inches away. The movement typically appears slow and deliberate, this isn't a quick snap toward the magnet but rather a creeping approach that takes several seconds to become obvious. If you place the magnet directly on the slime surface, the material will gradually climb up and around it, completely covering the magnet in 3–5 minutes.
The strength of the response depends on several factors: iron filing concentration, magnet strength, and slime thickness. A thicker layer of slime will respond more dramatically because it contains more iron particles working together. You can experiment with different filing amounts, some makers use up to 4 tablespoons for a more pronounced effect, though this does make the slime stiffer and less stretchy.
If your slime responds poorly, the most likely culprits are insufficient iron content or a weak magnet. Craft-store magnets simply don't have enough pulling power. Invest in at least one neodymium magnet if you want to see the full effect.
Storage and Longevity
Store your magnetic slime in an airtight plastic container or resealable bag. Kept properly sealed, it should remain usable for 1–2 weeks. The iron filings will eventually oxidize despite your best efforts, turning the slime orange-brown as rust develops. This is a normal chemical process and indicates it's time to make a fresh batch.
If the slime becomes too dry during storage, you can revive it by kneading in a few drops of water. If it becomes too sticky, a light dusting of cornstarch on your hands while kneading will help absorb excess moisture.
Don't flush magnetic slime down the drain or dispose of it in your regular trash if it contains significant amounts of metal. Seal it in a plastic bag before discarding to prevent the iron filings from contaminating recycling streams.
Frequently Asked Questions
Can I use iron oxide powder instead of iron filings?
Yes, iron oxide (Fe₃O₄, sometimes called magnetite powder) works well and produces a smoother texture with a darker black color. The magnetic response may be slightly weaker since iron oxide is less ferromagnetic than pure iron, but many people prefer it because it doesn't rust as quickly. Use the same quantity you would use for filings.
Why isn't my slime moving toward the magnet?
The most common reason is magnet strength. Refrigerator magnets or small craft magnets won't work. You need a neodymium (rare-earth) magnet with sufficient pulling power. The second most common issue is too few iron filings in the mixture: if you skimped on this ingredient, try making a new batch with more iron content.
Is this safe for young children to play with?
Children ages 8 and up can generally handle magnetic slime with supervision, though adult-made batches tend to turn out better. Younger children should be supervised closely due to ingestion risk. The iron filings make this slime more dangerous than standard slime if swallowed, so err on the side of caution with kids who still put things in their mouths.
Can I add food coloring?
You can, though the iron filings already give the slime a dark gray or black appearance that tends to overwhelm lighter colors. If you want a colored magnetic slime, add the food coloring to the glue mixture before incorporating the iron filings. Dark colors like blue or purple work better than pastels.
How do I clean up spills?
Fresh slime picks up easily from most surfaces: just pull it off in one piece. If it dries on fabric or carpet, try freezing it with an ice cube (which makes it brittle) before scraping it away. The iron filings can stain light-colored fabrics, so work over a protected surface.
Does the slime lose its magnetic properties over time?
Not exactly. The iron filings remain ferromagnetic indefinitely, but the slime itself may dry out or degrade, making it less responsive. Rust development can also reduce magnetic response as the iron oxidizes into compounds with weaker magnetic properties.
Disclaimer: This experiment involves materials that can cause irritation if mishandled. Adult supervision is recommended for children under 12. Iron filings may cause minor skin irritation in sensitive individuals; wearing gloves is advised. Borax should be handled carefully and kept away from eyes and mouth. Neodymium magnets are powerful and can pinch skin or damage electronic devices if used improperly. This slime is not edible and should be kept away from pets and young children who might attempt to eat it. Store in a sealed container away from moisture to prevent rust formation. Dispose of magnetic slime responsibly: do not flush down drains. As with any hands-on learning activity, use common sense and prioritize safety throughout the process. Tierney Family Farms assumes no liability for injuries or property damage resulting from this experiment.