You pick up your phone, catch the light at a certain angle, and suddenly there’s a line across the glass you’ve never noticed before. The first reaction is usually panic, followed by confusion: is that a scratch I can live with, or is the screen actually cracked? Working out the answer matters, because a shallow scratch is often just a cosmetic nuisance, while a true crack usually calls for a professional screen replacement. Knowing which one you’re looking at tells you whether you need a quick clean-up or a trip to a repair technician.
The good news is that you can tell the difference at home with a few simple tests and some decent lighting. Here’s how to read what you’re seeing.
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The Visual Difference Under Good Light
Lighting is everything. Take your phone to a window or stand under a bright lamp and turn the screen off so the display is black. A dark screen reflects light cleanly and shows surface marks far better than a lit one.
A scratch tends to look like a fine, consistent line scored into the surface. It usually runs in a single direction, catches the light as a thin bright streak, and sits entirely on the top layer of glass.
A crack looks different. It often branches, changes direction, or spiders out from a central point. Instead of a clean line, you’ll see a jagged edge or a splintered pattern. Cracks also tend to catch the light unevenly, with tiny flashes where the glass has separated.
Simple At-Home Tests
If the visual check leaves you unsure, these quick tests help confirm what you’re dealing with. None of them require tools you don’t already have at home.
- The fingernail test: Gently run a fingernail across the mark. A surface scratch is smooth and your nail glides over it. If your nail catches, dips into the line, or feels a distinct edge, you’re likely feeling a crack where the glass has broken.
- The water-droplet test: Place a single small drop of water on the mark. On a scratch, the droplet sits on top and beads normally. On a crack, the water can seep into the line or spread along it, because there’s an actual opening in the glass.
- Angling under light: Tilt the phone slowly back and forth beneath a light source. A scratch stays as a steady line. A crack will flicker and sparkle as different facets of the broken glass catch the light at different angles.
Checking Which Layer Is Damaged
A phone screen isn’t a single sheet of glass. There’s a protective outer layer sitting above the display that actually produces the image. Figuring out which layer is affected helps you understand how serious the problem is.
If the damage is purely on the surface glass and the picture underneath looks perfectly normal, you’re probably dealing with a cosmetic scratch. The display is intact and only the protective top layer has been marked.
If the line interrupts the image itself, distorts colours around it, or appears to sit beneath the glass rather than on it, the damage has reached deeper. That points to a crack affecting the display, which is a different situation entirely from a simple surface mark.
Touch and Function Clues
Sometimes the clearest sign isn’t visual at all. How the phone behaves can reveal damage that your eyes might miss. Watch for these warning signs:
- Dead spots where the touchscreen won’t respond when you tap near the mark.
- Flickering or a screen that briefly goes dark and comes back.
- Discoloured patches, coloured blotches, or lines of pixels that look wrong.
- Black ink-like spots that grow or spread beneath the glass.
A genuine scratch has no effect on how the phone works. It’s purely cosmetic. If you’re noticing any of these functional problems, the damage goes beyond the surface, even if the mark looks small.
When a Scratch Is Actually a Hidden Hairline Crack
The trickiest cases are hairline cracks that masquerade as scratches. These are fine, faint lines that look harmless at a glance but are actually breaks in the glass. They’re easy to dismiss, especially under poor lighting or on a phone that’s been in and out of pockets all day in the Perth heat.
The fingernail test is your best friend here. A hairline crack will almost always give your nail a tiny catch, where a scratch stays smooth. It also helps to clean the screen first, because dust and smudges can disguise a crack or make a harmless scratch look worse than it is.
If you’ve run the tests and you’re still not confident, it’s worth having someone experienced take a look under proper magnification. Some hairline cracks are genuinely hard to call without a trained eye.
Once you’ve confirmed the mark is a real crack and not just a scratch, you’ve answered the first question. But identification is only the beginning. The more pressing concern becomes what keeps happening to a phone when you carry on using it in that condition, and that’s exactly where the conversation turns next.