Magnetic Field Viewing Film 4"x4", Magnetic Flux Display, Magnet Pattern Detector, Scientific Project Teaching, Reusable and Automatic Recovery - Olive

This is the GOOD stuff, different colors show different field strength. Still doesn't indicate polarity (I've never found one that does), but it's so much better than the dark-green-or-black stuff.This product is laminated which makes it extremely stiff and durable, while the green-or-black is very thin and flexible, and easily damaged.Attached are two photos of the magnetic print bed on my Ender 3 Pro printer. The olive flim easily reveals two small defects where the bed isn't properly magnetized. When I put the green stuff over the same spot, only the smallest subtle hint shows that anything is wrong, it would be easy to miss the defect. Also you can see that the green stuff is already pretty beat up from handling, while the olive remains nearly flawless.

Works good, no issues.

The media could not be loaded. It is great for relative magnetic field strength. See video of what you can expect.

I purchased this on a whim and have been amazed at how fun it's been to explore magnets with. If you buy this, CHECK OUT A REFRIGERATOR MAGNET! I always thought those cheap magnets were unnoteworthy. It blew my mind to see (and then learn after some googling) that they're a clever arrangement of magnetic field domains known as a Halbach array, which doubles the field on one side (the back) and essentially cancels it on the other (the front). See the striped pattern in my first picture, and check out the Wikipedia articles on Halbach arrays and on refrigerator magnets for more info. For a cool effect, try stacking two fridge magnets and look at the interference patterns as you rotate one while holding the other steady.What caught my attention about this particular viewing film was its multi-color nature based on field strength (many others are monochromatic) and the fact that it "resets" as the fields are taken away, allowing you to see what magnetic fields are currently present and not some mess of the past history. The film appears to change almost immediately at room temperature (not sluggish) as you move a magnet. I don't know how fast it actually is, but I suspect it wouldn't keep up with very rapid changes.This viewing film came with a rigid protective plastic case and a little card showing a rough scale for color versus field strength. I'd take the numbers with a grain of salt, but the color gradient does add some nice qualitative information about the shape and strength of the fields. Colors indicate fields normal (perpendicular) to the plane of the film, and the neutral brownish-yellow color indicates either no appreciable field strength, or fields that are tangential (parallel) to the plane of the film. Although you can't differentiate between North and South, you can easily see where fields are concentrated and where the magnetic field direction changes.Also pictured on the included card is an indication of how the film works. Just guessing, but it looks to me like it might be a thin-film interference effect, where the interference region thickness (which sets the color) depends on how strongly pulled down the internal particles are (which depends on field strength).This would make a great gift for STEM-interested folks (kids and adults alike).

Crisp lines at the edge of the magnet and change of color extending beyond showing the field strength.I have an old hard drive magnet that shows two reddish fields about an inch away from the magnet. You put the film next to the magnet it shows blue/purple edges. green toward the middle and a one inch complex yellow field around the whole thing. A broken stack of magnets or the back of an iPhone is very interesting to look at.

I placed it between and alnico magnet and sensor and could hardly see the field. Sensor activates around 50 Gauss. I was hoping to see field pattern between sensor and magnet. I expected orange near sensor and light green near magnet. It was 1" diameter 3/8" thick magnet south facing sensor.

Nice to be able to see where the little magnets are in various products in case you want to do little modifications like drilling holes or cutting notches without wrecking the magnetic function. Also fun to see where they really are, how big, which direction N/S poles face, etc.

The media could not be loaded. This one does not have a memory, meaning it will only show up when the magnetic field is present. That alone makes it 10x better than the cheaper ones for sale. I ordered this one and a cheap $10 one from Amazon as well. The price difference is reflected in the quality and how well this works.It is completely encased in some sort of plastic covering making it very robust. Not sure what anyone means when they say it doesn't pick up anything but strong magnets. My best guess there is that they never took it out of the protective cardboard casting for shipping.I used this to verify a bad crankshaft reluctor ring, which uses magnets to create a signal to be picked up by the hall effect sensor. It is had ordered this sooner it would have saved me 8 hours of time, but I have it now.If you are just looking to play around and waste 10 bucks get the cheaper one. If you are actually going to use a magnetic flux film buy this one.