The MTG rip test exposes card stock by permanently damaging the card. Core color alone does not prove authenticity. Do not tear a suspect card, even as a last resort.
What is actually inside?
Wizards describes a blue adhesive center in its primary stock and also documents a different genuine multi-ply construction in Playing Card Board. That is more precise than saying every real Magic card contains one identical layer of blue paper made by a single printer.
A torn edge shows material. It does not establish who printed the card, whether it has been altered, or whether the represented edition is correct. A blue line is not a certificate; a non-blue result does not by itself prove a fake.
Why tearing makes uncertainty worse
You can destroy a genuine card while still lacking a conclusion. You also alter the item that a seller, marketplace, or independent examiner may need to inspect.
Ripping a trusted bulk common is not authentication of another card. It only reveals that particular common's construction. Do not use an expendable reference to invent a universal rule for other sets or finishes.
The documented rip-test limitations include genuine cards with non-blue cores. The practical recommendation is to preserve the card, not to search for a more dramatic destructive test.
What to do instead
Compare the exact version's printing on both faces. On suitable non-foils, a light comparison can provide additional information without exposing the core.
Inspect existing edges with magnification, but do not cut, scrape, peel, or bend them. If you suspect a reback or the results disagree, seek an experienced in-person assessment.
If the card arrived in an online order
Keep the card and packaging in the condition received. Photograph concrete differences, retain order records, and contact the seller or marketplace promptly for its review instructions.
Do not destroy or return a suspected counterfeit on your own initiative while a case is unresolved. The next useful step is better evidence, not a torn card.